Not saying I'll choose this class, but no scout? I'm more of an Ultramarine tactical or assault, maybe apothecary

Devastator or Apothecary. I've always been the support gunner or medic in Battlefield games, so it'll probably carry over to this.

I've never played a shooter game in depth. How would the devs incorporate the healer's (apothecary) mechanics in the game? Would the player have a HUD of the health of his squad? He would also need to move from one battle brother to the next to use his narthecium. And no collection of geneseeds...

Techmarine, depending on whether or not they can deploy turrets.

I voted other: My primary would be a Librarian given the chance.

To be specific: a Blood Angels Librarian.

I knew I was forgetting something.

Tactical marine through into Sternguard vet.

I look forward to firing a hellfire bolt-shell into a Tyranid and hopefully if i can use them against players, watch them dissolve Eldar, Orkz and Traitor marines.

Ultramarine Tactical, Space Wolf Assault, and another for Devestator. Not sure how I feel about the other classes, but I could give 'em a whirl. Rune Priest has me interested.

techmarine for me

Chaplains great combat bonuses and bad ass on the battlefield, Scout sergeants great long range sniping and sabotage missions.