I enjoy the kind of fantasy adventure that D&D lends itself to.
I tend to make characters with well-developed backgrounds, both to give me some role-playing depth and give the DM some adventure opportunities. Crunch-wise, I favor simple, but well-optimized builds for my characters. I will NOT make anything that breaks your game world. As a fellow DM, I'm just not interested in doing that.
I've been playing table-top RPGs for 20 years and probably have the best knowledge and enjoyment of D&D 3.5. On a scale of 1 to 10, I'd rate myself an 8-9 for experience; I also DM a lot. Let me be the rules encyclopedia for your game!
As far as maturity level, I'd rate myself an 8-10. My last group meta-gamed a bit too much for my taste, so I'm hoping to get away from that style of playing.