KMS and the other technologies that integrate easily into Xorg and the kernel are really nice. Not having to reinstall the nvidia driver after a kernel update is awesome. Back when I used an nvidia it always sucked to reboot into a new kernel and then remember that X won't work anymore. The nvidia driver also used to show an Nvidia splash scree when X started (probably still does), and that was pretty annoying even if it could be disabled.
For the most part I don't even need 3d when I use Linux. I just browse the web, read email, and write code and tinker around with my Gentoo system.
Whenever I feel like running a Windows game, I use Windows as much as I hate doing it. I used to be able to play games with wine when I had an Nvidia card, but it was a pain to do and wasn't really worth the effort anyway. I really hope wine gets better, but it's still pretty buggy.