These tips and tidbits make iOS 9 a must-have for me.

We've written our official review of iOS 9 and given you an overview of the operating system. "But Serenity," readers have asked, "What features are you actually using?" Hold tight, questioneers! I'm going to tell you in just a second.

I've been playing with iOS 9 since the very first beta. As such, I've had some time with the operating system to mess around with its well-touted keystone features and hidden tidbits—and to get bored with at least a few of them. The twenty features below are the favorites I'm still using, three months in—and the ones I expect to use many months after.

20. Making sketches in Notes

I've used Notes for years as a place to write down roller derby practice plans and strategies, but trying to explain drills to teammates with typed X and Os was... less than pleasant. Notes changes all that. Not only can I doodle when I'm bored, or build hypothetical interior design plans for our basement, but I can, at last, sketch out drills in a way that's not so ASCII-inspired. Thumbs up.

19. Zoom in on videos

Fairly straightforward, but a huge boon for (again) me and roller derby: iOS 9 brings pinch-to-zoom to videos. Want to see what someone's skates were doing? I can just pinch in on that section of frame and blow it up, and the video will continue playing. I've used this constantly during iOS 9's betas, and I'm so glad to see it made its way to release.

18. iCloud Photo Library now shows the size of your downloads and uploads

Since iCloud Photo Library's release, you've been able to track the upload/download status of photographs by scrolling to the bottom of the Photos tab. In iOS 9, you'll now see the actual size of those uploads, and how much has been synced. Love this. Very helpful for knowing how long my iPhone should stay on Wi-Fi when syncing images.

17. Siri's beep has gone vibration-only on iPhone

I love using Siri in secret-agent mode—AKA, pulling my iPhone up to my face and quietly whispering to it. Unfortunately, Siri's chattiness—even over my device's headset speaker—made it a little too noisy for public usage. I'm thrilled, then, that Siri's signature double-beep has been replaced (on the iPhone) with a double-vibrate; moreover, when you enable a Siri setting, you can even silence Apple's assistant from verbally chatting with you unless you're connected to a Bluetooth speaker. I've launched so many more apps using Siri at my local coffee shop, and every launch has been glorious.

16. Check your battery and your friends' whereabouts in Notification Center

Two notification glances I've been wanting for ages—battery and Find My Friends—show up in iOS 9. (Battery, unfortunately, requires a paired Apple Watch.) They're great. The Battery glance shows your current battery level, but also the level of any connected accessories. Super helpful! The Find My Friends glance gives you an abbreviated overview of your contacts, giving their current location (if available) along with a colorful "Miles/Kilometers away" bubble. Tap any contact, and you'll be whisked away to the app itself.

I love both of these glances, and use them constantly. Great system additions, and very happy to see them make it into iOS 9.

15. The Music app's "More" button doesn't suck

When the Music app launched with iOS 8.4, its More button was... lacking, to say the least. Not so much in features—the More button had plenty—but that lengthy list was less than aesthetically pleasing to the eyes. Now, tap the More button and you'll get a much more organized bar with very-obvious "tap to launch the album this song is from" miniature cover art, along with new buttons for favoriting and sharing. As a frequent Music user, this button is wonderful; I've been holding off talking about its wonderful powers for a few months now, so I'm delighted it's finally come to the general population.

14. Tap and hold the refresh button in Safari for content whitelisting and desktop sites

Safari's "Request Desktop Site" button is great—it premiered with iOS 8 and I've used it constantly to reload non-responsive design websites with terrible mobile options. But it was a little hard to find; you had to tap the search bar, then drag down the search list.

With iOS 9, Request Desktop Site (and its new iOS 9-exclusive companion, Reload Without Content Blockers) has moved behind a tap-and-hold on the refresh button in the toolbar. Far fewer taps in a much more convenient location. What's not to love?

13. The iPad's keyboard-as-trackpad

I am so mad that this didn't make it onto non-3D-Touch iPhone models for iOS 9's general release, but it's still a great feature for the iPad (and for the iPhone 6s/6s Plus). Rest two fingers on the iPad's keyboard when you have text content open, and it instantly becomes a trackpad for cursor input in your text. It's smart, dead simple to use, and makes the process of editing text on the iPad oh so much quicker.

12. Siri Suggestions in the Search screen

I didn't think I would use Siri Suggestions when Apple first pitched the feature on-stage at WWDC—it seemed too fiddly for my taste, and I rarely used the Search screen except when launching apps from hard-to-find folders. Boy, was I happy to be wrong. Siri Suggestions are pretty good for apps you want to be using or people you want to be texting, but where it actually shines is in Maps's Nearby integration. Using Yelp's database, Siri Suggestions tries to find you the best location for food or entertainment depending on your routine and time of day. I use it constantly to find and try out new food and coffee shops, and I'm having more fun using it every day.

11. Using Siri to turn off Low Power Mode and launch apps

While Siri's technically had app-launching capabilities for a few years now and Setting tweaks since iOS 8, Apple's voice assistant's new silent beeps and faster response time means that I can call up hard-to-find apps lickety split and turn Low Power Mode on or off with a simple voice command. The future is pretty cool.

10. The Shift Key works again

All hail our new lower-case keyboard overlords! While I probably would have preferred a return to the blue-highlighted Shift key of iOS versions past, switching the keyboard from upper-case to lower-case works about as well. This change has saved me from numerous typos and improper caps lock—especially when live-tweeting roller derby games! Apple Keyboards team, take a bow.

9. Content blockers are great

I know what you're all going to say. And before I get resounding cries of "hypocrite, you write for a site with ads!", let me explain. In general, I support paying for people who do good work, even if that means viewing advertising. But what I highly dislike is tapping a link from Twitter while on the go and spending 30 seconds for it to load—only for it to load with an ad interstitial that I can't dismiss for another 30 seconds. No funny cat slideshow is worth 60 seconds of loading time. Content blockers like Crystal give me the option to avoid waiting endlessly (and wasting my cellular data) for silly Twitter content. If I like what I see, I'll just tap-and-hold on Safari's refresh screen to bring up "Reload Without Content Blockers" and visit the site again.

There are also plenty of excellent content blockers that don't block the entire web, instead focusing on more specific targets. Hide and Seek, for example, shields your identity when using Google's search services, so it can't build a picture of who you are from your search terms.

8. Photos's smart folder for Screenshots

Forget selfies: The Screenshots smart folder is where it's at. I've been asking for an automatic search of your photos for any PNG-based screenshots since I started doing ebooks—it's just easier to find images that way—and while the Screenshots folder may not make a big deal to your average human, it's a thrill to have it on iOS 9 now. (The rest of you, enjoy a collection of your front-facing photos, labeled Selfies! That's cool too, I suppose.)

7. Notifications are sorted by date

Another long-standing peeve (are we getting into a pattern here?): In iOS versions gone by, trying to figure out what notifications were recent and which you needed to pay attention to was a chore if you attempted to use Notification Center. Notifications were grouped by app and organized poorly, which often meant buried GroupMe alerts and game requests. As of iOS 9, you can force Notification Center to display most recent notifications at the top—grouped by app or otherwise. I switched this over as soon as I could and have been using it every day. It's glorious.

6. Return to previous app

I'm a woman of habit, and with years of double-pressing the Home button to switch apps under my belt, I did not expect I'd easily switch over to using that little back button for the previously-viewed app in the upper left corner. And initially, I was right: I spent the first two betas steadfastly ignoring the shortcut. One weekend, however, I took the time to solely try and tap the Back link when switching between programs; after three days, I never looked back.

Return to previous app is so much faster in practice than double-pressing the Home button—even with the new multitasking screen. It's a smart little shortcut, and once I got used to actually tapping it, I wondered why I'd ever been stubborn about the Home button.

5. Low Power mode

There are few things I do with my iPhone more than drain its battery. I'm a heavy smartphone user—in large part because I'm almost always testing something for my job—and that often results in an iPhone with just 15 percent battery life going into the evening. So, I'm not kidding when I say that iOS 9's new Low Power mode has saved my bacon on numerous occasions during the last few months. Part of me is tempted to just keep it on any time I drop below 80 percent.

Low Power Mode is essentially one switch that turns off all extra battery-draining backgrounding on your iPhone; flip it (or tell Siri to do so), and instantly, your battery stops its deathly descent. It's saved me hours of battery life before, giving my iPhone a last extra gasp of life so that I could get it to a charger. Previously, I'd have used Airplane mode; instead, Low Power mode allows me to keep in touch with friends and colleagues and continue working without fear of my battery giving out at any second.

4. Car-triggered estimated driving directions in Maps

As someone who routinely drives several hours to get to practice in Boston, I adore estimated driving directions. I've used in the past (and still use) a great program called ETA that gives you live traffic estimations for your destinations, but there's nothing quite so satisfying as turning on your car and getting a "Traffic to Home is 80 minutes right now" alert with built-in driving directions on swipe.

It took a couple of weeks after installing my first beta to see my first Maps notification—the device needs to learn your routes before suggesting some to you—but was delighted when I finally did. It's such a painless way to see my route home, and getting that estimation allows me to decide whether I want to wait in the Boston area awhile (to let traffic die down), or immediately hop on the road (to take advantage of the lack of cars). I know people who drive a lot and don't like the alerts, and you can turn them off pretty easily from Settings > Notifications; for those of us who often go one place for long periods of time, however, these are a wonder and a joy. And they trigger on any car Bluetooth connection—you don't need a CarPlay receiver.

3. Maps search is good! Actually, honestly good!

I've loved the look of Maps since its release, but Apple's directions application has been... less than stellar in the past when it comes to actually finding points of interest and accurate directions. I won't say things are perfect in iOS 9—no mapping app can ever be perfect—but Maps has gotten tremendously better at directions, alerts, and telling me the best places to eat that are open for breakfast right now. It's using Yelp's recommendation engine along with a bunch of under-the-hood programming for its new Nearby search, and I've been constantly impressed with it. Contextual search is better, too; no longer will Maps send me to India if I just type in "Roll On". (It actually knows there's a skating rink in Massachusetts with that name, now.)

2. Find all saved passwords in Safari

Hip hip hooray: If you, for whatever reason, have multiple accounts on a single service, you can now see every stored password you own for that site. The Mac has had this for years, and 1Password on iOS has been making it fairly easy to view your stored passwords, but it feels different and special on your iPhone. It's a great feature for power users and social media managers alike, and I find myself using this pretty much every day.

1. Swipe to highlight images in Photos

There are few things I reserve a "Finally!" for. This is one of them.

Swiping across a group of photos to highlight them seemed like an obvious trick to me back in 2010, but it took until iOS 9 for Apple to implement the feature. I'm so very glad they have: It's such a nice way to select or deselect images, and it's much quicker than tap-tap-tapping your way to an AirDrop file.

Your favorites?

I've left out a couple of bigger features I use constantly—Split View on the iPad being one—but I'd love to hear what you folks are finding in iOS 9 so far that you love and helps you work. Let us know below in the comments!