Although Remniscient of Doom 3, and AvP2 this game is a bit dissappionting...
This game has excellent possibility, although from what I played it is excessively hard from level 2. The game is fun, and challenging, but once you meet up with these dog-like creatures, it gets excessively harder. On level two there are plasma shooting baddies. They are not that hard, except when you get two or more shooting at the same time it bogs my GeForce 6800 XT down so much I can't move very clearly.
Overall, this game has high potential but doesn't quite meet it. The top-down view on the world is a bit dizzying, and the enemies are too hard. Maybe if VALVe could make a different game with this engine it would succeed more. Don't get me wrong, it's fun, but it's a bit too hard.