CS:S pisses me off. I never really understood buying guns in it, and there are plently of more up-to-date fps games out there. I'm not terrible at it, but 90% of the time, the other team will have a few people that exploit and play unfairly, and its just not really worth it to me.
TF2 is a game i'm bad at, lol, but it is still a ton of fun.
GMOD doesn't really fit in with the other two, since it isn't just an fps. It is pretty glitchy, but there is a ton more that you can do in it than in most games.