Commenting on suggestions:
Runes of Magic is pay2win, and boring. Uses the typical "gear+skill rotation=skill" formula. Would probably also kill your laptop anyway.
Perfect World games are alright but Perfect World itself feels VERY dated. I couldn't stand the combat. It was terrible. Appearance customization is good though. Forsaken Worlds seems like PW but updated, but it'd kill your laptop I think. Not to mention they're determined to go through 900 closed beta phases before launch.
Mabinogi...yeah. It's more of a casual/social game. I despise the combat system. It's bland and annoying more then anything. But social aspects of the game are fun, and it has some interesting systems in place.
I'd stick to FPS though.
Team fortress 2 and Counter strike source are honestly the two best multiplayer FPS out there. CSS for more serious/realistic FPS playing. TF2 for more hectic, fast paced teamworking multiplayer.
Both are cheap and neither require much to play. CSS in particular has very low requirements.
TF2 seems to be going strong with updates, and both have huge playerbases. (CSS in fact, is the most played game on Steam, even beating CoD:BO by a lot).