A few of my favorite things from testing the RTM version:
1. DirectX 10 (obviously). I don't think this needs explaining, but look at these pics:
2. New GUI. It looks pretty. Flip 3D is really cool:
3. The search doesn't take like 9 hours like it does in XP.
4. Better security?
5. Networking is easy to setup. Haven't actually used it, but so I hear.
I did notice that it wasn't quite as snappy as XP is, but it's only the prerelease RTM version that I was using, so I figure by the time of the official release, they'll have that fixed.