Any form of leveling RPG is actually so boring to me these days. WOW is great for a bit, but the amount of grinding you need to do to actually get 'better' at the game is mindlessly tedious.
Personally, I think COD is more sociable. You can talk and play with your friends, whereas with Runescape for MOST people it intends to be random people. The gameplay is also more exciting and more realistic.
The reason why it isn't considered nerdy is because most people play it, whereas only a few intend to play Runescape (obviously there a millions who do but in comparison to COD probably not as many!).
at school, it's generally the popular boys who shout about playing COD and they think it's cool. Runescape on the other hand, you don't admit to still playing it :| that was cool in year seven...
but that's just how other people view it. In my opinion, they're both as equally nerdy and you're basically sitting in front of a screen doing stuff that isn't real. But I love both games :P
It's simple. COD has gone mainstream. Even lads play it now, so its no longer nerdy.