I think Vista is decent. I am rather neutral on all of the changes other than perhaps the Start Menu. But, honestly, even back to Win98 the Start Menu was fine to me and file indexing has never been all that useful to me. I'm more of a console guy anyway, having grown up with DOS and spent lots of time with Linux.
Vista really bogs down my old laptop's Radeon 9600. It's much slower in games than under XP. On a card with framerate "to burn" (for now), it's not as noticeably slower. But whatcha gonna do if you want to run the upcoming Direct3D 10 stuff. Hopefully not all of these games will be slideshows, unlike the current releases.
I would be perfectly happy with XP w/ D3D10, but of course, MS obviously didn't want that to happen. What we really needed was to have OpenGL win the API battle. That's the OpenGL consortium (or whoever they are)'s fault and game devs faults. MS sucked them in and now we are suffering from the API monopoly. OpenGL had its chance, with the half decade that D3D was trash, but it just didn't work out.