But the Astartes are broken in 40K. I think the main reason why that is is because everyone has a MArine Army. I switched to guard a long time ago. And 3+ armour save for all are so annoying. They should all be 20 points, not 15. Necrons are even more obscene, the army for failed marine palyers (which is saying something). So yeah. Guard are so much easier to characterise with. Them and orks. Guard v Orks or Guard v Guard are some of the best matches. Especially in cities of death. With my close-combat orintated urban catachans. Oh yeah...
But going back to the idea of a 40K shooter, I think there would definately be amarket for a 3rd Peson Tactical where you are a Tanith Ghost. And you could choose your specialisation, Scout, Sniper, Flamer, Comms, Assualt, Support etc. You could have a charcter for each, like Mkvenner, Larkin or Nessa, Brostin, Beltayn, Milo, Rawne, Caffran, Criid, Bragg or even the big man.
I think that would work.
Oh, and bolters fire ROCKETS. Bolts are rocket powered, and can change their flight path. Best guns ever.