Same ol' same ol', albeit too short. Keeping it simple.
It starts where you left off, giving you a nice sequel feeling, picking up the action as well, and then suddenly while you're drawn into the action it ends. Sadly because more of Half Life 2 is what we fans were dying to get, although as little as it was provided, proved to be enough, for the moment that is.
I downloaded it from steam with no problems (I couldn't wait for the next day to pick it up), decyphered it, and played it flawlessly (although some unusually long loading times were experienced).
Having the newer graphic cards allows you to get a different feeling to half life, with the introduction of HDR, which by itself should be enough for serious fans to get the game, like myself.
The game engine seems improved, considering the release date for Half Life 2.
So in the end, if you liked Half Life 2, you'll "briefly" enjoy it's "sequel".