I did not think assassin with sniper rifle and melee weapon is good for some reason: CQC with tank? Of course! Ranged figthing with a commando holding a commando (WTF?)? Of course!: Assassin will be invincible.
Sorry for the double post but I think a deathwatch can greater with larger maps, more roof, and like in Counter strike, you can unlock weapon using money you earn killing ennemi soldier, or a class system like in call of duty with killstreak to unlock airstrike or ammo drop. An online mode can be good to. (sorry for my bad english)
Create an outpost, two hospital with auto resurection, auto deploy marines, when they are very numerous, send them, they destroy evrething on their way. Theorically, you can deploy infinite amount of marine