The Win 7 UI is actually very nice (IMO) -- arguably one of the nicest. It doesn't look like much in screenshots, but it has a definite quality to it. I can't really comment on the quality of apps or other aspects of the system, but the UI is quite slick.

It is, however, a bit boring to use for extended periods as it seems quite consistent across apps (again, I have limited experience). It's like seeing the same thing over and over again.