I think this is the worst Half-Life game in the series, but it doesn't mean it's bad: I like the helpful characters and the fact, that Barney Calhoun isn't the hero like Gordon Freeman and Adrian Shepard. There's no G-Man, but he doesn't have to appear at all, but there are crossovers with Gordon Freeman. So the characters are a bit better than in "Opposing Force" I think.
I'm quite disappointed with the level design: There are lots of long corridors with little variety in enemies and surroundings. There are less weapons and no new enemies. It's also a short game (maybe even shorter than "Episode One"?)
7/10
