I voted for little light. In the day time, I usually have the lights off and blinds shut. It's enough to see what I'm doing and I don't get any glare from the windows. Plus, I'm more focused on the game than what's around me if the lights are off.
If it's nighttime, it depends on how I'm feeling. Sometimes if I feel like being comfy, I shut the lights off, get in my pjs, sit under a blanket in my special video games chair and listen to my ipod (Unless I'm playing Zelda or Super Mario Galaxy 1 and 2, because I'd rather listen to the game in that case
). Sometimes though, I keep them off if I don't wanna play in the dark. It all depends.
But just like when watching movies, I get more into it with the lights OFF.