Test Track is a great ride. But I think it gets a lot of votes here because many (including myself) were expecting so much more. I love it, but I can see how some are disappointed when they finally ride it.
Along those lines, I think The Many Adventures of Winnie the Pooh is my biggest disappointment. Just like TT, I think the ride is nice, especially if you are a Pooh fan, and my kids love it. But when I first heard about the concept (i.e., being in one of Pooh's dreams) and how much was spent to make it, I was really expecting a lot more. The first time I went on it I was kind of like, "OK, its Snow White with different characters. Why not just keep the Toad?" Anyway, it's cute, but its just a track with some animatronics. Where all that money went (I forget the number), I have no idea. The Department of Defense must get these contracts.