Bits I liked:
* Alyx. Brilliant! More good AI buddies in games, please! She deserves a bigger gun though.
* The first bit where you didn't have a gun. Really atmospheric, I liked it in HL2 as well.
* The section in the barn with the helicopter thing shooting the building to pieces.
* The sniping bit, that was cool. If you've got a buddy they need to do useful stuff like that.
* The escorting bit near the end - lots of backtracking but the playing field got modifed each time.
* HDR - it makes a difference. I love the whole Eastern Block post-apocayptic art direction and this shows it off well. Some nice normal mapping too and the faces are lovely.
Niggles:
* Levels on a much smaller scale that in HL2, a bit cramped, no vehicles.
* Zombies in the dark with a flashlight.
* The electric water jumping puzzle. Leave the platform jumping to Mario.
* A few too many "stick the car on the antlion hive" sections
* Bad guys (especially Zombines) don't seem to react to gunshots until they die. This is really distracting now that I've played game where they do react.
* No plot advancement. Are your actions doing anything? What's going on? Does it matter? As per HL2 all the plot seems to have happened before you actually start the game.
* Hard mode - they've just made baddies tougher and weapons weaker rather than making the game harder. In hard mode it feels like you're walking around with a double-barreled Bic spitball launcher. Normal mode is the only way to play.
Anyway, it's an excellent game, if short. The level design is tight throughout and there's some nice new ideas in there mixed in with the older ones. Roll on Episode 2!
