I think I felt very similar really. The challenges were quite a nice touch but I think ultimately it felt a little too frustrating and shallow as it went on. Of course I should point out I haven't completed it yet either, I think I've got about halfway through and haven't felt the need to return to finish it for a while.

Saying that, I wasn't a massive fan of Braid either but I did finish that. So if someone asked me which I thought was the better game I'd be hard pressed to give a definitive answer. I think Braid pips it, just because it was at least straightforward enough to basically finish if you didn't care about getting all the extras.

I reserve the right to change my mind on a whim though, if I ever replay the two/finish Winterbottom in the near future.