Vista also adds a few new games to the roster. Plus it gets rid of those stupid internet-enabled games as well! That alone is a significant improvement.

One new UI feature that popped up in a few places was this new dialog box. Each individual option seems to have it's own button now, even though none of those things look like buttons until you mouse over them.
The other thing that this feature gives you is extraneous descriptions and comparisons of things which, granted may be useful, but just make these dialogs harder to read and forces them to take up more screen space. Like I keep saying, display real-estate is not infinite.

Doing any file operations now display fancy graphics with glass panes flying about.

Help now requires an internet connection. Fortunately there are still a few local help files, but this is stupid.

Search has been completely redesigned again. There is now a little search box in the upper right like a web browser.