A recent UseNet thread in rec.games.board about Space Hulk reminded me how much I love that game:

Whenever I played this game I always took the marines because everyone
around here assumed the game was unbalanced toward the Stealers. And I'd
always kick their asses. :)

There are three things to remember when playing the marines: Speed,
speed, and umm... oh yeah. Speed.

The strategy for the Stealers is, of course, to slow down the marine
player. If you can get him to waste a couple of turns not making
significant progress toward whatever goal, you probably have the game. I
have found most marine players to be a bit timid, so on those occasions
here I played the Stealers, I made them paranoid and also kicked ass. :)