Reno is pretty laid-back and generally takes things in stride, though if something does piss him off, he will have no problems with saying something about it. He's loyal to his friends and protective of them, though in a sort of passive way. (Not that he has any friends here yet.) I wouldn't call him a happy person, but he gives that appearance most of the time--he can look at life and laugh at it.
I hope that helps. I find him a particularly difficult character to describe in some ways, but I think that sort of covers it. Let me know if you have any questions.