WinFS is my biggest disappointment. It also looks like security will still be a problem which frankly is inexcusable.
The final page of a beta review
here summarises some of it. (Do check out pages 1 - 4 for the rest of the review though).
I did read a very thorough web site documenting the what the author considered the six major features of Vista and the subsequent demise of five of them. I can't find it for the life of me now though, if I stumble across it I shall certainly post it.