I'm shocked nobody is talking about Rise of the Blobs. Sure, on the surface it looks like a cutsie match-3 reserved for children, but that's just to get you to lower your defenses. Once you've dismissed the game, that's when it steps on your face. This plays like a puzzle game from before some marketing firm invented the label "casual," back when puzzle games required intense mental focus lest you let the game liquefy your mind.
Basically, you're a little marshmallow dude that's trying to get rid of multi-coloured blocks on a 3D pole. That means you need to rotate the pole around to ensure the blocks don't overtake you. And you also have to manually trigger the explosion of blocks, leading to some deep-ass combos. Also, every time you think you've got the hang of the game, it throws you a new mode that tweaks the mechanics just enough to ensure you don't go lipping off about how your a Blobs Master.
The game is free, apparently. And no, the IAP doesn't get in the way. You can pay money to unlock modes immediately or buy one-time powerups, but your mind is stronger than that.
http://appshopper.com/games/rise-of-the-blobs