Braid
Braid is a time-bending puzzle game disguised as a simple platformer like Super Mario Bros., and has enough self awareness to make several references to that fact. Beneath the basic gameplay controls and pleasant, hand-drawn appearance though, there is an incredible amount of depth and inventiveness to every aspect of the game's design, from the time manipulation mechanics to the devious puzzles to the great story. Basically, there are five normal worlds you can run through. The goal is to get all the jigsaw puzzle pieces inside each one, and put them together to finish the ambiguous pictures and move forward towards the ending. The pieces become more and more difficult to get to, and finding them requires you to make use of that world's unique brain-twisting trick.
The first level just introduces rewinding time, which you can use through the whole game. The idea is nothing new to games, Prince of Persia: The Sands of Time and Blinx: The Time Sweeper were doing it years ago. But no other game has taken it to such an extreme like Braid. You can rewind all the way to the beginning of the area, and as soon as they begin throwing in objects that are immune to the power, things start to become crazy. Further levels add things like the world's timeline being controlled by which direction you're moving and a shadow clone of you that repeats the actions you did in between the last two rewinds. Learning how all these different tricks work and ultimately using them successfully to do something that looked impossible is one of the most satisfying feelings I've had playing a game this year. Even when something's confounding you at the moment, you still feel like the solution's right there because it usually is. I'm not going to pretend I did every puzzle by myself, but even when getting help you can appreciate the genius behind some of the ideas. There are a couple little things that prevent the gameplay from being perfect though, like a single puzzle that you can't solve the first time you see it when this would have been easy to avoid, and a moment here or there where something you didn't expect undoes all the work you just did.
Besides all that though, a big part of Braid's appeal is the presentation. The music and graphics merge to create the perfect environment for the story, slightly whimsical but with a certain dark edge that doesn't become clear until later on. Everything in the game works for the story, in fact. A lot of it is revealed in vague bits of text before each level, but that's mostly flavor for the real plot, which can be interpreted in a number of ways. What's especially great is when the quirks of the time manipulation work in the story's favor. Little moments like the end of the world where time progresses with your movements are great touches, and the final level is one of the most brilliant things I've ever seen in a game. A scene plays out that you see from multiple perspectives, and the way it all fits together is remarkable. After that there's an epilogue that reveals a little more about what could possibly be happening, but that last level is amazing enough to end it right there. The combination of intelligent puzzles and storytelling make Braid the best download-only game I've experienced. I played it on a friend's 360, but when it gets released on PC in a few months I'll pay for it myself because it's totally worth it.
