World of Goo

Alternately, the best game to come out so far this year.

It's ... hard to easily explain why this game is so amazing:
It's the simplicity - The game's closest analogy is probably Lemmings, your goal is to use goos of different types to achieve your goal of saving the rest. The game has an almost perfect learning curve, putting new things to you, but with hints on how to do things and never very hard at first. The game does get difficult toward the end, but the game provides you with a number of level skips you can use. If a level stumps you, you can just return later.
It's the amazing atmosphere - The game has an amazing art style and does a lot with it. When you first hit the fourth chapter, you'll be amazed. Also, the sound effects are used to great effect, making me think of Worms. The goos don't speak, really, but they do emote. They giggle, make noise, etc. It's incredibly cute, and you attach to them (... No pun intended.). And, ah, the music. The songs, while short, are great. Finally, the game's story/plot/symbolism. A puzzle game with plot, you say? Yes, I do. It's told via the signs and a few short cutscenes. It's amuzing, in a similar way to portal. It's nothing amazingly deep, but it's cool. Each chapter end level is something different and weird, not hard.
It's how great of a puzzle game it is. As I said, the difficulty curve is amazing, but you'll see levles that, at first, you have no clue how to do. It took me some messing around, but for all the levels I did and most of the levels I skipped (Skipped due to getting incredibly close to the end, having the goostructure collapse, and being out of timebugs), I didn't have to look up a solution to any of them. And for some of the levels, you'll feel like a right clever bastard after figuring out the solution and implementing it. Most of the levels have a great solution.

Really, my first line says it best. You owe it to yourself to play this game.