HL2 Episode One offers a very short, but highly entertaining experience. It may even be better than HL2.
GAMEPLAY: Half Life 2: Episode One has more of the same awesome gameplay that HL2 had. Except there's more of it in HL2 Episode One and it feels more intense. Enemies can now grapple down buildings and they seem to be smarter this time around. There is a new enemy -- a zombified combine soldier which adds more challenge. There are numerous puzzles throughout the levels which will take more time to figure out than the ones from HL2. Alyx is by your side throughout the entire game this time and she is very helpful. Although some of the things she says are kind of stupid, she is great with a gun.
GRAPHICS: The graphics in Episode One are almost the same as in HL2, except for one huge difference. The HDR lighting in Episode One makes this game seem so much more realistic. There are still the annoying hiccups where the FPS drops significantly for a moment, but they are much more uncommon than last time.
SOUND: The audio in Episode One is pretty stellar. The voice acting is top-notch and the music is pretty good. All of the guns and effects sound pretty much the same, but that's not a bad thing.
VALUE: Value is the only problem with this game. It's over before you know it. There are only five levels, so you can finish the game in an afternoon. But, since this is just part one of three, it is to be expected that the game is short.
Half Life 2: Episode One is an excellent installment in the Half Life series. It has even better gameplay than Half Life 2 and better graphics. The only problem is how short the game is. I will say though that it ends with a cliffhanger, so expect more episodes.