I played this on UV difficulty and it was okay, if a bit repetitive, until the final episode (4 levels). At this point it became seriously frustrating with contrived ambushes at regular intervals involving revenants or archviles (3 or 4 at a time, even 6 on one occasion). "Expert placing" of enemies is all very well, but when done so perfectly and artificially, creating endless crossfire and triangulation situations, it just becomes tedious. In level 29 you are faced with three cyberdemons and a spider mastermind in a cramped inescapable arena, with inadequate ammunition and 30-40 revenants at the perimeter firing homing missiles. In the unlikely event that you survive this, there's an almost impossible 'timed lift' gimmick to exit the arena. Might have been alright as a 12-15 level game without the stupidly difficult finale.