I gess the best move is to get World of Warcraft, as I've only heard good things about it (not that I hear alot of news about it anymore).
However, if you do get into any Massive Multi-Player Online Role Playing Games prepare for the fallowing:

Addiction
Time wasted
Plenty of hours everyday palying
Peeing in a bottle

Alot of good things about playing MMORPG's, alot of bad side effects (like lack of social life and such and such).

fr0g got it right.