When it comes to gaming, in-app purchases are a tricky thing. Some games use Apple's mechanism to wrest more cash out of you to complete levels faster; others enrich the game experience with new costumes and player characters; others still use the in-app purchase to build off the original game.

It's that last option that has come to Monument Valley, ustwo's brilliantly-constructed architectural puzzler. The Escher-homaging app first appeared on the iOS App Store in April, winning a number of awards shortly thereafter — including Apple's own prestigious Design Award at the 2014 Worldwide Developers Conference.

Monument Valley was one of my own favorite iOS games to play back in April, and I've been eagerly awaiting its expansion ever since I heard rumors of its existence a few months back. Was it worth the wait and the $2 purchase? Oh, architectural gods, yes.

Monument Valley: the appendices

The original Monument Valley told a twisting, slightly eerie tale of a forgetful princess winding her way through her intricately-built and strangely twisted lands, now filled with odd black flightless birds. I won't spoil the ending of the original ten-level game here for those who haven't yet completed it — though seriously, stop reading this and go play it now if you haven't.

In contrast, Monument Valley: Forgotten Shores focuses more on feelings than it does narrative — it's designed to live within the world already constructed by the original game rather than expound further with prequel or sequel storytelling. As a result, each of the seven appendices can be played in any order, though you can't reach the expansion's final level without completing them all. (There's even an appearance from everyone's favorite mystic ghost halfway through the extra levels that playfully hints at as much.)

The game's new levels may not build their own story, but that doesn't mean they're merely outtakes or reused material. It's very clear that these appendices sport just as much craft, level-building, and wonky physics as their predecessors, if not more. There are new bizarre feats of architectural wonder; strange interactions with thieving crows; and even a heartbreaking moment or two. (Without giving away too much, the stage in question struck me much like the later levels of Thomas Was Alone.)

There are those that are protesting ustwo's $2 charge for this expansion — that think anything new in the Monument Valley universe should be theirs for free. Everyone is entitled to their opinion, I suppose, but here's mine: Those people are fools.

Building a great game is monumentally difficult. Expanding it without destroying the magic of the original is even harder. Given the hours of work that went into this game and the delight it brought me upon playing, I would have paid $20 for Monument Valley and its expansions — I feel stupendously lucky that I can get the whole thing for $6.

I can't wait to go back and play this expansion again — my first crack at it took me a few leisurely hours of spinning and puzzle-solving — but in the meantime, you should go check it out.