Just thought I would write a little about this game since it did come out while E3 was going on. I've only played a couple hours of it, but so far I am pretty impressed by the game. I still say the Source engine does a really good job in game experience over a year since the release of Half-Life 2. I hope to have more once I actually beat the game, but so far I am enjoying it and think it's a pretty good pickup for $20 via Steam (or at your local store). I have no idea how long it is, but nothing quite beats seeing the main bad girl in skimpy clothing right at the beginning.
Remember that HL2 Episode I is only a couple weeks away from being released as well. That should be just as exciting and Valve has said it is their best single-player experience yet (which is high praise coming from them).