Here's a few tips for those who have trouble playing the Marine.
Do not play him defensively. Play him like you are the biggest badass (Thanks Leydenne!) on the block. Strut like you've got the stuff. You own this facility, and no alien scum are going to take it from you. Run into combat like a berserker. Melee early and often to make sure you do not get heavy attacked. If an enemy heavy attacks as their first attack in combat, immediately press your block button after you get hit (the Marine will put his gun up as soon as it is possible, so don't freak out if he doesn't for a split second, as he is still recovering from the staggering heavy attack). After you block the light attack (which WOULD have killed you), throw a melee and then kill them while they are down. This works the best against aliens.
Use the shotgun. Use it as much as you can, and use the heavy attack (fires both barrels) like you've got unlimited ammo. If you hit a predator in the face (Even from a few yards away) with the heavy attack, it will instantly gib them in a spray of delicious green glow stick blood. Against aliens using the double barrel is a bit more difficult, as they are fast, but just slow down a bit and wait for your chance.
Do not, under any circumstances, use the flamethrower. It is absolute rubbish.
I'd say controlled bursts.
No, the drop in accuracy is actually helpful at longer ranges when you fire nonstop BECAUSE they are either invisible or hard to see. Just keep firing and watching for blood. At close range, firing like a madman works just as well, since you ought not to be missing at such a close range anyways. Besides, you have 99 freaking rounds. That's a LOOOOONG time to fire.
Also, I'm open to some games, if anyone wants to play.