Well I finished HL2: Episode 1. It definately improved in the end. There were some excellent action sequences involving you vs. vehicle combat that was pretty exciting. There were also several squad-based encounters with groups vs. groups vs. groups that I definately enjoyed. I was pleased that it improved as it went.
However, the ending was... Incomplete. As far as the story goes. Even more so than HL2 itself -- which was pretty contrived. I'm gonna have to go to Episode 2 and see just what the hell is going on.