NEOTOKYO° is a Half-Life 2 multiplayer mod.  Kinda plays like Counter-Strike mixed with some manga, Ghost in the Shell immediately came to my mind.  It's got a learning curve, but it's meant to be realistic and teamwork oriented.  It was also featured in the "Mod World" section of the September 2009 issue of Game Informer. 

Recently a new patch was released, adding some maps and some other gameplay changes.  No matter how I describe this mod, I wouldn't be able to do it enough justice -- it's one of the best mods I've ever played, for any game. If you own Half-Life 2, you pretty much owe it to yourself to download it and check it out.

 

For more info, check out

www.neotokyohq.com

http://www.moddb.com/mods/neotokyo