I personally think Halo is kind of crap, the computer aims for you ( I know there is a option to turn it off but still, why even have that option for a online game? )
If you're playing consoles I would suggest the Metal Gear Solid series, it's the best series for PS2
Starcraft is cool, there is a new one coming out in a few months or so and it's going to be really cool!
Diablo 2 has too many cheaters :haha:
World of Warcraft is only fun on private servers because it's free
Half-life 1, 2, episode 1, episode 2 ( coming out soon ) are
THE best computer games ever made.
Counterstrike ( 1.6, CZ, Source they are all good ) for computer is really fun FPS.
Company of Heros is a really really fun RTS game made by Relic, it's fun online but the single player is sort of short but the Skrimishes will last forever so it's non stop fun
Also The Elderscrolls Series ( Morrowind and Oblivion + all the expansion packs ) have alot of gameplay, I played Oblivion for total of around 350+ hours on my Battle mage
-TPX