ok, I tried this game a few times over the last couple of nights. What I have found is that I suck at using any of the two handed guns. I have just been playing Veteran with 3 Bots. When I use pistols, any combination with no upgrades, I can finish Veteran levels with ease. Once I try any of two handed guns, I struggle. With the Shotgun I find the reloading to be terrible. In the heat of the moment, it's very hard to tell when you have reloaded properly. With Assault rifle and the MT Rifle, they are so hard to aim. And I have upgraded stock and sights on the Assault rifle!! Haven't tried an SMG yet.
The biggest problem for me, however, is that I just don't think it's much good.