Maybe too short, but some of the best gameplay I've experienced (spoiler-free)

User Rating: 9.4 | Half-Life 2: Episode One PC
Episode One has great gameplay. Some say that it ends too soon (it does), but I'm glad that Valve decided to distill the great aspects of HL2 into this tidy package instead of including its less fun aspects just to make a longer game. Less fun aspects of HL2 for me included Ravenholm, the long vehicle sequences, and too much "super" grav gun at the end of the game. The "super" grav gun made the end of HL2 too easy, but it didn't feel that way in Episode One. Indeed, Episode One was tougher overall, combining puzzles and combat well. Nothing felt repetitive either. Also, there is some replay value because Valve included commentary for the game (a la a DVD commentary).
Also, battling the combine with Alyx was a welcome addition. She has a lot of great lines and definitely saved my butt a few times. Perhaps at times she seems too powerful. During the game I thought that she should have died, but she just shook off the zombies crowded around her.
Graphics were improved for Episode One. The environments felt more detailed. HDR was done to great affect too. There were a few battles where I caught myself squinting to see enemies in the bright light. Very cool. Also, shiny stuff actually appeared shiny. On the other hand, I saw Alyx's white shirt glow as if it were creating light when we were in the Citadel. A bit weird.
The story was advanced fairly well. Lots of new questions though. Valve seems to be adverse to the typical "boss" fight now. That trailer for Episode Two is such a tease! Hopefully, Valve gets it out by Christmas, but I won't hold my breath.