This level is ruining a great game....SPOILERS

I didn't particularly love the level, but I enjoyed it and didn't really have any problems.

Are you using any possessed weapons on that level? If you haven't been leveling up possessed weapons, I highly recommend it, for they really help in areas like this. I always make sure that my possessed weapons do elemental damage (I prefer fire and Inferno), but I also make sure they have stats like health on crit and health on kill, and I try to add stats that increase the crit chance for the weapons. Usually I gain health on every 3-5 hits. I also level up my crow wrath abilities to the max, and the murders of crows will give you health and potentially freeze your enemies, slowing them down. I noticed that the enemies of this "dungeon" do drop quite a few health potions, but with my possessed weapons, if it was just waves of the fast enemies, I could quickly restore my health just by fighting them off with my possessed weapons and crows.

You've probably already noticed, but any time you hear the horn, a new wave of enemies arrives. If you see one of the glowing exploding demons, shoot them down first, focussing on scatter shots. Keep running and dodging backwards until it explodes, and it will take out any of the hoard nearby. Then mow down the little guys. Rarely do enemies spawn from behind you when the horn sounds, so as soon as you've heard the horn, retreat to an area you have cleared out. If you can, put a wall to your back and force the enemy to come through hallways or other narrow parts. This method takes quite a bit of time, but your chances of survival are far greater.

I was also at about level 18-19 and had earned about 3 additional skill points by selling relics to Ostegoth, so I might have had an easier time than others. But I can see where this level COULD be annoying. I hope this helps.