At first glance, 10000000 doesn't look like anything to get excited about. If anything, its title should immediately give you a headache - how many zeroes is that again? (It's 7, by the way.) Spoken 'ten million,' this puzzle-based RPG was released to a very warm critical reception on iOS last year (and later Windows / OS X), and has been a hit ever since.
So, what's with that title? Actually, ten million is the score you'll have to achieve on a single 'run' to escape the castle our unnamed hero. You don't have any direct control over the character, you simply match up 3 tiles of a single type in the puzzle below the dungeon to deal with situations your hero encounters as they arise. This may mean a sword to fight off an enemy, a key to unlock a chest, or a spell.
Your character's 'equipment' essentially makes the tile-matching game easier / different and modifies the mechanics of specific abilities; making attacks more powerful, improving the chance certain tiles will appear on the board, etc.
At $2, this is an eminently reasonable entry fee for a title that has enjoyed such critical praise - it's one of those games that you really do need to play, if only to experience it.