I'm glad most of Doom so far is set on Mars because the Hell landscape can get a bit drab after a while. The Mars complex is varied and have all kind of cool machinery while Hell is a huge brown hill.
I think I'm halfway thru the game and I added the Plasma Rifle to my Combat Shotgun rotation, which is basically all I need until I run out of ammo. It's not to say the other weapons are bad but those 2 so far deal with all kinda of problems.
And I see why people say Glory Kills get repetitive after a while. I'd gladly accept a toggle so you could just melee the enemy with no camera change. It's a good idea which perhaps the Bethesta team liked a bit too much.