Classes do matter in space since you get a space ability every x8 level, but aye, not as much as it effects ground.
I personaly liek my Tactical officer, sure i dont get no fancy turrets, shield generators and viral nanobot thingymajigs to hide behind. But i get to put points into rifle, and i get to use my big gun to blow your head off with extra damage
as far as i can tell, tactical are the only ones whos skills improve basic weapon damage.
I went through the tutorial as as tact... tossing grenades was... oddly enjoyable. lol
Im considering making an "alien" orion to do Engi as well, but Im afraid that if I do, and I get too far into the character, Cryptic will take that moment to release actual Orions for feds in the CS. >.<