Card Ninja - just the name conjures up interesting ideas as to what the iPhone (and iPod touch) game might be. As it turns out, the ideas may not be that far from the truth.
In Card Ninja, you are simply "flicking cards" to the appropriate goal post, based on color, pattern, or some combination of those. The flick motion is simple enough, using the same kind of flick that you do to scroll through your contact list. The cards are all set out in the middle of the screen, with goal posts are various locations (the harder the level, the more goal posts you have!). The goal is to flick them correctly (not just slide them over, you lose points for that), and keep you card count higher than the minimum number to advance to the next level. If your card count drops, the game is over.
The game is fun, and the flicking cards can be fun. I found after continued play, however, that my fingers started to get a little sore. So perhaps long term play is not a good idea - I would limit yourself to an hour at a time.
The game play, while not complicated, is engaging, and trying to speed up your reaction time (seeing the card, deciding where to flick it) can be a significant challenge. I found myself getting flustered a few times and that would just make the game worse - one mistake seems to compound on top of another. Adding in things like wild cards just makes it reach another level of difficulty.
Unfortunately there is no multiplayer. I can envision a great multiplayer version, with people flicking cards at each other trying to beat your opponent. You can compare high scores online, but there is nothing like a head to head competition to get the blood boiling...or bring out the ninja in you. They have updated the game in the past, so perhaps that would be coming out in a future version. There also is a free version to try before you buy, so give it a shot.
All in all, Card Ninja is an entertaining, unique kind of game that can pass away the time - if you have the reaction time and finger strength for it. The game is engaging and the upper levels can be a challenge. While there is no multiplayer, for $.99 it is a fun game to try, and I give it four out of five stars.