I tested it and I got some results.
Difficulty: 9.99999/10 HARD AS HELL

When i saw the imps coming with lightning fast I was like WTF and I shoot a lots of rockets to them but they still kept coming. That part was really hard. Boss part too.
Gameplay: Same as doom.9/10
Man that ammonution is good.Don't even try to fix it, its cool. I finished it with enough ammo and I think its very well designed.
Map designs: Very good ! Keep going
By the way the way to kill the boss is very hard. You must make him shoot the skuls over the little ramps around. If you do them both 2 platforms will raise. They got a skull switch. Press them and DOOM WILL COME.

Really after that its incredibly hard its like survival. o_O