Downloaded some mods for hl2 last night.. it does work with a hacked version of the game once you have the emporio game loader.. The HL2 mod scene looks to be more promising than HL1 or most other games..
Source Racer: Basically a cross between mario cart/wave race , racing on beachers , through sewers or in an obstacle course , powerups include nitro , jump and a weakish weapon that pushes enemy racers away from you... like mario cart you run over a wierd thingy for power up and can use it later.... but lots of ramps , speed boosters and jump boosters all across the area .... I'm not sure if the development team is continuing to work on the game but the Beta 2.0 that i have supports multiplayer (over lan!) and has enough maps to keep you going for a good while.
Only drawback would be the physics are a little too bouncy.. if you boost into a wall at the right angle you will go bouncing around for quite awhile.
Ant Lion Troopers : A single player mod insipired by starship troopers... your dropped into a combine outpost and must defend the base from an assault by hundreds of ant lions, using simple squad commands and turrets its alot more fun than you'd expect.. would make a good multiplayer game , only problem is that at some points early in the game when most of the combine are alive ( 20+ soldiers) and the ant lions start to rush the AI load starts to lag the game....
Anyone with HL2 will want to play both these mods... Maybe Source Racer can replace some of those Oldie goldie wave race games with some shiny graphics and dread physics....
http://www.fileplanet.com/100511/0/section/Single-Player << file planet HL2 mods..
http://downloads.vgpro.com/pc/halflife2/srclient20.zip Source Racer