There are several broad "rules" for this type of game. The biggest is this - the more players on the marines side, the more backstabbing, dropping your mates in it, running away and sheer cowardice/selfishness you're likely to see. I don't need to tell you how much this adds to gameplay

I'm with you n815e - lots of good boardgames out there. Level 7: Omega Protocol is worth a look. It's a Privateer Press boardgame (with minis) for dungeon crawlin' bug hunts, but it has some interesting features.
It's a co-operative game pitting one or more marine players against an "evil overlord" player. The good guys use Adrenaline Points to perform actions. One of the features of the game is that the player who controls the monsters also gets to use any adrenaline points spent by the marines. They can use those for a range of actions, or build them up for an extra special effect or group of monsters. There's a ton of options there, limited by the scenario.
So the more the marines do, the harder the lair fights back. Do the marine players go in fast and hard, or try to use a bit of brains and do things quiet-like, using skills and avoiding trouble?
As well as the different types of marine (each with their own special abilities that affect the game), there's a ton of equipment options for the good guys to make the game more interesting.
The old Aliens boardgame was great - I believe the components are all available for download on Boardgamegeek. Go for the advanced rules - ammo tracking isn't difficult, but it does make things nasty for the marines.
And yeah, Space Hulk!