I just played it, and it's quite impressive.
The point of "Lost Coast" isn't the gameplay. It's a technological demo that happens to have some combat. In fact, I wasn't expecting any fighting at all. I was just interested in the scenary and checking out the new engine. To be honest, I was a bit annoyed by the combine.
I very much enjoy the commentary. I found them very informative, and they really enhance my appreciation for the technical aspect of the rendering process.
I took some screenshots. As far as the aesthetics, I was actually expecting a bit more from Valve. The water looks even more gorgeous, but I think some textures do not work well with HDR. And the distant fog effect is not perfected yet.
Overall, I was quite thrilled. I am just glad that my machine could handle the engine. I was given a warning that my specs weren't up to par, but luckily the game ran without a hitch.
w00t!