Fear multiplayer is a good one. There's trackmania nations, which features a nice level editor, and online/lan competitive play, as well as single player practice.
http://www.joinfear.com/main - Awesome!
http://www.trackmanianations.com/indexUk.php - Danger! Appears to take you through time travel. Sponsored by nvidia for the world cybergames competitions or something.
There's the clasics from gta
http://www.rockstargames.com/classics/gta 1, 2 and wild metal country.
Having a ps1 like gamepad helps in wmc - pretty much deathmatch with tanks. I played this freshman year of college with a few friends. Slow pace compared to say, quake, but fun.
gunbound - like worms. One of few freebies i haven't tried, but it's in my download folder
http://gunbound.ijji.com/ - rated highly.
Never tried getting into America's army. If you take it up, let me know how it goes.
http://warrock.net/ - like bf2, squad based, and pretty well received. free.
quake 2 - coop (good for 2 player, loads of fun, no cd key)
quake 3 - cdkey, but I dont think it cares if 2 people use the same one.
Ground Control -
http://www.fileplanet.com/promotions/groundcontrol/ - AWESOME!
S.W.I.N.E -
http://www.gamershell.com/download_11942.shtml - Okay
Warrock -
http://www.warrock.net/index.php - Quite Good!
Zsnes, an snes emulator, will permit playing multiplayer snes games, over the internet. you may need haimachi vpn for it, I don't know.
There's tremulous
http://tremulous.net/about/sounds like a quake 3 engine rehash. Free. should be fun
downloading it now. ... Not bad! Fast paced, required reading that manual to tweak it i'd say, but nice work.
Side note offpost as a response :
The point of a game is to have fun.
There are none? Come on Shiv, surely you jest?
Guildwars is a beautiful game. Levels doesn't meant squat. You're supposed to get to 20. The power of your character is made through skills you've acquired. Two friends of mine and myself, have all three episodes and swap between that and WoW. If you don't like it, it's merely opinion. We've played that for nearly 3 years, and they've added so much since it's inception. playing to level 12 gives you barely a hint at what playing the game would be like. Getting there in one day vs having your level 20 with multiple secondaries, and loads of nice skill combos for each situation with proper heroes, etc, organizing with friends to get through rough areas - torment, underworld, hard mode, urgoz warren - the fun is in the game itself, NOT the character. We play certain levels over and over because it's fun, and often a good challenge.
WoW has no competition with GW because it's just too different. Different mechanics, different tactics, different style. they may be part of the same genre, you may look down on your character from above and control him, killing enemies around you, but that's as similar as you can call it.
Now as far as the comment on random socializing goes, yes. Popular games = population, and popular games are commercial and cost money
That part is quite true.
BTW : Not saying free games are crap, or even as good as commercial games, but they can be quite fun, and there's a lot of mileage you're able to get today sticking to them.
