Great start to a great series.
The game requires Gordon Freeman to shut down the citadel's destress beacont o the Combine "advisors" and to deliver the information about the signal to Eli Vance and essentially escape the crumbling cityscape.
The visuals are still the same as HL2's but do include some new anti-aliasing options (mainly x16's and x8's) and higher resolutions to deliver a more optimum gaming experience for newer machines.
As Episode One is the first in the HL3 series, it IS quite short so to make up a whole entire game with Eps 2 and 3. Nevertheless, Episode One does have improved physics and this become evident as we see Dog (Alyx's machine thing) jumping off buildings and rubble as well as throwing, yes throwing, Gordon and Alyx across a canyon... in a car.
This is a must have for any HL2 fan, but if you didn't really enjoy your HL2 experience then I do not reccomend you invest in this game.