I saw this first on another site, and watched the conversation/speculation there. What I've been able to figure out is:
-The video is definitely made in the Netherlands; there's Dutch everywhere and the viral site ends with ".nl."
-There's a definite "Half-Life 2" vibe from the whole video, and not just from the sounds and music: the high-def video of the HUD news crawl says things like, "Millions feared dead - No news from disaster area - Largest single collapse in history since Black Mesa." So it could be set in the HL universe, but where it fits in the timeline is still under debate.
-There's a very strong chance it's not a Valve game at all. The video could just be using sound clips from the HL2 archives because they're easy enough to use. Heck, I did a zombie movie back in college using nothing but sounds extracted from the game.
-EDIT:
Also forgot, the viral site has a lot of credits with "Tim" in them, but one of the credits, "TIMSMIT" brings up the name "Tim Smit" on Wikipedia... apparently a Netherlands' bio-dome expert. Not sure if that has any relevance yet.