DinoHunters

To quote from the Kuma website...

DinoHunters is a free work of fiction that combines hilarious scripted sequences with stimulating first-person shooting. Using the hottest game engine and other sophisticated entertainment tools, DinoHunters combines comedic television-like movies with exciting game play in a revolutionary entertainment medium.

It is a free game which could be classified as "advergaming" as the game has a real life sponsor in the form of Schick Quattro razors. Players do not need to own a copy of Half-Life 2 in order to play.

The DinoHunters website is a rather amusing spoof of the whole reality/dedicated TV channel genre.