I've finished Braid today and I thought it was just brilliant. I also had trouble with "that one puzzle" and agree that I was a bit disappointed by the general lack of difficulty in most puzzles, but it was still basically ideally enjoyable. Interestingly, contrary to an earlier comment in this thread, I actually liked World 6 the best, because I really liked having an additional object to use alongside the normal time manipulation.
By the way, I limited myself to playing through one world each day and I can very much recommend that (I just apparently forgot about that rule for the last two worlds, it was just too intriguing
). While finishing it didn't take me much more than about 5 1/2 hours in total, playing it for about a week and not just skipping puzzles I didn't understand immediately really enhanced the experience for me.
I'm just quite a bit disappointed that I didn't "get" that one specific quote in the epiloque, simply because I hadn't heard of it before. Still, the whole finale was excellent.
Summing it up, I think Braid really is a special game and very much deserved all the hype it got.