I thought I'd like Opposing Force, but I did not. It's certainly an interersting concept that appeals to me, the chance to play as a HECU marine during the Black Mesa Incident and be on the side of the "bad guys" is a cool idea in my book, and although Opposing Force opened strong, I felt that as it went on it became progressively weaker. I think that where this game fails the most is in the gameplay. There are way too many weapons that you can carry around in this game (16 in total) and it gets to a point where either you forget to use them or they are redundant. I found myself sticking to the basic, dependable weapons the whole time (shotgun, assault rifle, etc) and there was never really a time when I had to switch to those alien weapons. I should also add that the barnacle gun is pretty much useless except for a couple of pre planned sequences where you have to go across an area using it, so that gun doesnt really see a lot of action which is dissappointing because it would have been cool to grapple up on regular ledges (not organic ones) and get a different view of the battle/tactical advantage. the AI in this game is also rather stupid, your marine buddies who are supposed to tag along with you (and offer you things like health etc.) will either get killed in about 10 seconds or glitch on a wall and stop following you. They're honestly better off dead so that you can take their guns and move along. The story is also pretty much nonexistent. No one bothers to explain where "Race X" comes from (and why Gordon didn't see them in his travels) and the same applies to the Black Ops enemies. They are part of the military, shouldn't they be HELPING you? What reason would they want to kill you for? And that boss battle, geez... what a boring waste of time. Whoever came up with that sorry ♥♥♥ excuse of a boss battle needs to be fired (there's nothing fun about shooting 2 eyes out of a monster). So, overall Opposing Force is an expansion pack that sets out to be as grandiose as the original Half-Life, but fails on its delivery. It's 5 bucks, so at the end of the day it's your choice as to whether or not you think its worth the pick up. But in my opinion, it's not really worth it.