Quite a fun map! I played on UV and had a pretty good time. The looping progression was satisfying and the combat was cramped but not stifling. The dark imp does a lot of work here, being a monster that goes down relatively easily but challenging your space more than a standard imp, making it possible to balance available resources around low/mid tiers without simply upping the monster count or starving the player too much to deal with healthier monsters. I also appreciate the little bits of flavor that add a nice sense of place to an otherwise abstract map (Those lava spouts turning on and acting as archvile cover are an especially good touch.)
My only major complaint is that some of the ambushes were a little mean, not giving very much time to asses the situation before you were as good as dead.