As of Friday, I had got 51 puzzle pieces, which slotted into 5 puzzles of 12 pieces each. Saturday morning, I was going to play "just a little farther", with the expectation that I'd get stuck and then frustrated, and get up and do something else. Instead, by noon, I had got to the epilogue and pretty well explored it. In talking with a coworker today, I guess I hadn't completely found every nook and/or cranny.
This is the best game I've played since Portal, and there are some easy comparisons that aren't all that interesting - both games involve some strange dimensional manipulation; Portal folds space, Braid manipulates time. More interesting to me, as a developer, is that each of them were playable well before they shipped and incubated for a long time. Each were made by a small team, and would be a really hard sell for a traditional publisher.
Braid (and, to a lesser extent, Portal) represents what games should be - giving the player an experience they haven't had before, giving them tools they haven't had a chance to use, and giving them new things to think about. Various people (notably, but not exclusively, politicians) have claimed that games are not art. I have a hard time coming up with a workable definition of "art", but Braid explores emotions and the human condition as well as any poem I can think of, it encourages discussion and interpretation as much as any piece of literature I've read. It seems to be making money, but if Jonathan Blow doesn't break even, he's still succeeded at delivering something close to his original intention.
I trust that if you've got an XBox 360, you've at least downloaded the demo. If you don't have an XBox 360, come over to my place - I'll clear the crap off the couch and make you play it.