I'm at an IT conference this week and used the Oculus Rift about 2 hours ago. I'm still dizzy. It will definitely take some getting used to. I know I was sitting still, but my body thought it was moving.
The demo they ran for me wasn't graphically impressive at all. It was very simple in the graphical style of WoW, but slightly more cartoony. It was an on-rails demo, I was the passenger in a side car on a motorcycle. The guy running the demo had to keep reminding me to look around. I kept remaining stationary like I was watching a movie.
Looking around though was really cool. At one point I ended up on some railroad tracks and the attendant asked me to look behind me. Like 10 feet away was a train chasing us down and gaining on us.
The hardware itself was really solid and felt like a finished product. I really didn't notice the extra weight so I think extended gaming won't be a problem.
After seeing the demo I'm really excited for the possibilities this brings. Games will definitely be way more immersive, but I will be worried about motion sickness and the time it will take to get over it.