IIRC in the later games you can change Shepard's class if you want to. However I ran Soldier on my male Shepard and I thoroughly enjoyed the experience, particularly in ME2 where the wide variety of weaponry available made it stupidly fun to play, and also in 2 and 3 Shepard gets the ability to eventually pick one of his team mates skills and use it himself even if he's not a biotic or whatever. Soldier Shep + Domination = oh yes.