MAP23 - SHOWDOWN
Pretty meh as slaughtermaps go. None of the fights are too challenging, except for some that might just be frustrating because of height differences or unfair traps. The Arch-Vile room just screams to be played by running in, grabbing both keys, hitting the Invuln sphere and then trying to run out while being blasted in the air. Sitting there just killing everything with the BFG... meh. The highlight for me was seeing the walls lower with the texture being improperly fixed so that it looked like the bricks were just slowly vaporizing from the top down.
MAP24 - DIEHARD
I wouldn't really call this a slaughter map since the fights all seem relatively small. Yeah, there's definitely a lot of high-end monsters (barons, mancubi, revenants, some archviles, a cyberdemon, etc) but there's only 132 monsters in UV mode, and ~12 of those are shotgunners/imps/demons in the first room. It does have a Living End vibe, and the map feels oddly short given the cavernous design, though. Decent map.
MAP25 - CESSPOOL
Wow. This map lives up to its name... and not in a good way. First time I played through, I spent more time figuring out how to open the doors to the first pool areas (turns out you need to shoot them) than playing the rest of the map. Once I got them open, jump in the pool, grab the yellow key, jump into the other pool, hit the yellow switch, easily kill some monsters, kill the spider and run into the exit. The imp teleporter worked but the other one didn't do anything and the exit was open. I ran through it a second time and got even more confused, because this time the second teleporter near the exit spat out a bunch of revenants and an Arch-Vile, and none of the exits were open.
And of course, this is all on top of the fact that the deep water trick (which I've always found annoying) is used throughout the entire map, and it makes the map a joke since monsters can't see you inside of it. (Was this not playtested?) And that stupid timed door trick... ugh.