As Poorchop wrote, frantic is a good description. The zombies everywhere do a good job keeping the player moving; zombies being around without an explosive weapon to immediately dispatch them- or another enemy to fight them- always makes me uncomfortable and anxious. Unfortunately, in this case it's easy to take big chunks of damage between them and the Grunts, and the easiest way to get some breathing room is ducking down and getting the Quad in the slime after clearing out the Grunts and Enforcers, then taking the double barrel shotgun and killing as many of them as you can before it runs out. Not entirely sure where else that Quad would be put to use, honestly, nor why anyone would think to intentionally dive in the slime in the first place.
Biggest complaint is probably the water pit where you have to find/shoot the button before you drown- the only reason I didn't die here was reading about it ahead of time (but not spoiling the rest of the map), it's a royal pain trying to get a good angle on the button even with a zero-spread weapon like the nailgun. Trying to swim to the surface only to be forcibly pushed back down by a trigger_push is sort of a kick in the crotch. Also: armor. Even a green armor would be helpful when clearing out the rooms at the start, and if you don't find the yellow armor secret you're not gonna have a fun time for the rest of the map after.
Never figured out how to get up on the last platform where the zombies were; probably could have rocket jumped but didn't want to risk the health chunk what with the kill counter saying there was still enough enemies left for a fight, only to find it was the end of the map, so I'm guessing that's due to the rotfish kill count bug. Overall not bad at all, pretty enjoyable outside the few issues above.
Skill 2 demo here: 10:06, 3/3 secrets, 102/117 kills.