SUPER EDIT!Subvein has now been renamed to Mutant Factions and version 1.0 was just released! Check it out at
http://mutantfactions.netSubvein is a top-down multiplayer shooter with guns, skills, missions and more. You play as a mutant and unlock crazy skills, fight in PvP arenas and kick heaps of ass! The game is completely free and only 18MB so you can start playing in minutes. It's a shooter like Counter Strike, but what makes it unique is that you play as a mutant and can unlock crazy skills. Invisibility, Bullet Time, Regeneration, all of these skill add plenty of depth to the combat and make things very fast paced and tactical. You can play game modes like FFA and CTF and will soon be able to buy vehicles too! If you like the sound of this you should check it out here:
http://subvein.netCheck out these groovy screeenshots to see what I mean:

Here you can see I'm using a skill called Bullet Time. This makes enemy bullets go slow around me, allowing me to dodge them!

Check out my sweet bazooka shot. He thought he could run away with the flag...

Here we are playing the Extraction game mode, which is basically like Capture the Flag but has multiple objective types.
Anyway, that should do it. Go check it out if you think you might like this. It is free afterall ;)
Get it here:
http://subvein.net