This game is fantastic...
It has the elegance, beauty and soothing nature of Lost Winds coupled with the mind bending and simply outstanding puzzle and level design from Portal.
The game in a nutshell is a platformer / puzzler. But to disregard it as either of these is simply criminal.
When playing Braid you become entranced to its charm (and frustrated at the levels occasionally!). You can't die and you can't fail this game, there are no time limits, no rushing or button mashing; the game feels like a sweet dream and a good night's sleep.
The puzzles themselves play with time much the same way as Prince of Persia sands of time does. But whilst the platforming is simpler (it is after all, a 2d game) the puzzles are much more challenging.
The best part is you can actually just exit a level and leave the puzzle until later (though you need to solve it eventually to collect the reward).
I have almost finished it (currently 58/60 puzzles solved) and I have to say I really loved it. A bit pricey at 1200 points for a 5-6 hour game but then some games retail at that price now.
Plain and simple, PLEASE at LEAST download the demo...
Here is a vid to give you some idea:
Gametrailers.com - Braid - Three Easy Pieces Gameplay
(I specifically chose a low spoiler vid as solving the puzzles is the point of the game)