The good things are the installer includes up-to-date drivers for new hardware (compared to XP), which is only to be expected from a new operating system. The installer is also ridiculously easy to go through, similar to many Linux installers, and initially asks for a small set of information then runs through the entire installation process without needing human intervention. A huge improvement over XP's incredibly dumb installer that required someone to actually click buttons several times through out the install (usually about 10 minutes apart).
Apart from the installer the system is also reasonably good looking. The Aero interface is nice and polished (literally) and many of the user interface changes are for the better, although they take some getting used to. For example, the new menu layout, the fact that what appears to be the "shutdown" button is actually the "sleep" button, the search bar on every windows explorer window and so on.
The truly bad things are pretty far between. Driver support is still a bit sketchy but I managed to get all the hardware working without any major issues. I dislike that you cannot have the single user on the system automatically logged in if they have set a password, quite unlike most Linux systems. The control panel seems a bit all over the place for a few items as well, like graphics options being spread around between Windows components and nVidia programs.
I think the reason I'm not impressed with Vista is just that … it's not very impressive. It's got a lot of nice things and works fairly well but most of the new stuff and improvements are things that other operating systems have had for ages or were simply dumb design decisions make in previous versions of Windows that really should have been corrected long before now. Even the slick Aero interface isn't really impressive when you compare it to Compiz/Beryl (which has been around for a while now and runs on much lower specced PCs), to say nothing of it's overall uselessness.
I should mention that I installed the copy of Vista Home Premium that came with the Dell so perhaps the other versions (Ultimate?) have more niceties. I also admit that I haven't spent that long digging through the operating system (only a few hours) so there might be some hidden gems lurking in there. Apart from that though I'd highly recommend not upgrading from XP just yet!