Expansions are never as good as the original, but this one is still fun and has a good length to it.
So the question; "Is this game worth the purchase." Yes and no. Now that it is old and you can get it used at GameStop or some place like that, then I would say Yes.
After playing the first game I really wanted to revisit the story, and the expansion attempts to do that but in a kind of retarded way. You play as a totally different group of insurgents, but your character has all the same moves including the awesome slow-mo effect, which hasn't gotten old.
The game starts adding some weird see-through creatures that it never explains, they kind of take the place of the annoying pop out ghosts from the first game. I never understood how a ghost could hurt you, but whatever. And they add a couple of different enemies but for the most part it is the exact same game, except that the environment, graphics, pixel and shading depth all feel a lot cheaper. Like most expansions, it truly feels like one.
But with the bad new said, I enjoyed the game and have played both expansion sets through twice now after playing the original first. And I have to say they feel like a very good length in time. I rarely get a chance to play a game straight through anymore, so I spent a couple hours a day on it and it took about a week or so to finish both expansions.
So not bad, maybe one of these days I'll try and play all four straight through the weekend.