Half Life 2
Firearms: Source brings the best aspects of Firearms to the Source engine, and then takes them a step further. You'll see a host of familiar weapons and maps, but you'll find the streamlined game play to be faster, focusing on aggressive, skilled play. From nearly the moment you spawn you can expect to be engaged in furious action.
Oh, and did I mention this mod is loaded to the hilt with beautifully detailed firearms.
This is a new video by the Fire Arms: Source mod team that shows some gameplay footage and some new features.