My 2 cents:
Sure, Death Mask wasn't real FPS like DOOM which was extremely popular that time, but this game was playable fast on an A500, had super sound (MiniGun anyone?) and music and featured also 2 player mode.
Even A1200 was too slow to run playable FPS games. That said, I played AB3D through with a stock A1200 and oh boy it was hard. With accelerator, the game becomes more playable and easier.
I think it was an interesting idea to mix Dungeon Master and DOOM.