Happy Hills is an interesting title -- it's similar to the awesome iBlast Moki 2, though it's not quite as good or as well-produced as that one. The way it works is that you need to use a series of bombs to blow a set of obstacles off of "hills" (which are actually columns with eyes, in an art style very similar to a Mario Bros. background), thus putting them in the titular mood.
The puzzles eventually break down to physics, as you've got to clear off the hills in as few bombs as possible. You can also blow certain blocks up into specific places to earn stars, and there are a few different types of bombs and blocks to play with as well, each with their own traits and strengths. As I said, the game isn't quite as fun or complicated as iBlast Moki, but it's colorful and has its own sense of puzzle-y enjoyment, as you can blast blocks across the screen with abandon.
There are 48 levels included in the initial purchase, and other level packs you can pick up with 48 levels each, so there's plenty of content to go around. There's full Game Center integration for leaderboards, and the title rounds out well, with some nice musical tracks and fun, simple graphics. Happy Hills isn't bad -- if you're looking for something a little more simple and carefree than iBlast Moki's sometimes extremely complex levels, give this one a look. It's 99 cents on the App Store right now.