Congratulations!) Cool game!
I have tried Nightmare! too once in this version and found that it's easier than in previous ones, mostly because new tactics system, increased powerups/good items spawn rate, and 1.2 exp bonus. It's not a problem to be berserked or invulnerable most of the time, so running through levels is a lot easier now. Unfortunately i died on level 19 because was surrounded by BoHs without phases or meds left. Just increasing quantity of monsters, or their quality won't help, you ignore them mostly. Lowering spawn rate of powerups could work. Also, Kornel, please explain me, why mosters ressurection time isn't constant? Sometimes enemy rise just after you killed him, sometimes you wait for ages before he ressurects. Make ressurection time constant and make it not too low, lower spawn rate of powerups, so player won't be able to just run through, and he would be forced to choose carefully every his next step(without rushing because it won't be possible that after 2 turns all that BoHs that you just killed, will arise).