So I played as a Marine almost exclusively tonight to see if my Marine problems were just me, and I think it was mostly my poor Mariney skills.

Though I still think it svcks that any attack stuns a Marine, but I
think meleeing an Alien/Predator stuns them. I've had a hard time testing it out since most of them just want to rip my face off. My only other problem with the Marine is how useless the shotgun and flamethrow are. I unloaded a whole clip from the shotgun into an Alien that was about 5/6m away (based on what the motion detector says) and it still managed to live. I'm almost positive I hit it every time because of it's screams/blood splatter (though it is possible that another Marine was shooting it at the same time and that I was missing horribly

). The flamethrower on the other hand is just freaking useless, I stood
right behind an Alien as it instakilled a Predator and held down M1 the entire time, then chased it with it for a couple feet. Not only did it survive, but it didn't catch on fire or anything! I can deal with the not-catching-on-fire part, but surviving that? C'mon now! The pulse rifle, smart gun, and single-shot rifle are all pretty slick though.
After my Marine runs, I decided to switch to Predator. Playing as a Predator is a lot easier in this game than the previous for me, and I think it's because the wristblades are so powerful now. I don't even need to find the plasma caster or the smartdisc, I can just run around slicin' and dicin'. I'm not gonna lie though, I feel pretty sweet running around constantly switching vision mode and hearing the "swoosh, swoosh" sound. :hehe: