I was able to briefly play the Battlefield:BC2 demo. However, I didn't get time to finish it. Here are my brief impressions:
1. The game seemed to run at 1024x768 resolution
2. There wasn't any noticable input lag using mouse/keyboard and video quality seemed almost native.
3. However, there was an instance of slight video lag for a second, which got me killed. There is some ocassional screen tearing.
4. Multiplayer is dsiabled. If you select it, you have to input your EA account and a CD Key. You are able to see the server browser if you already own it, but it will kick you out if you select one.
5. There were a lot of short cut scenes in the beginning mission, which was kind of annoying (ex. Cutscene->shoot a couple of dudes-> short cutscene->shoot a couple of duded, etc). This all happened in the first 15 munites of me trying the game.
6. It's limited to 30 minutes.
7. I was kicked out of the game while I had it paused for 3 minutes. It told me that my bandwidth dropped.
8. This uses much more bandwidth than OnLive