And so begins my frustrating journey of not being able to get important switches to open. It's a small little map, and I probably would've found it decent except that I could not get the switch that opens the red door (in singleplayer) to open. Yeah, I can get the far one with the Arch-Vile to open, but that's coop only - no way to reach the red door from it. No idea how to get the close one to open - had to noclip to get through.
As others have said, it's very... square. Big large buildings that you can actually go inside, which is cool, but the outsides are bland and empty. Empty can be fine and even impressive if done right (think about some of Unreal's vistas) but when it's just a bunch of boxes... yeah. Not a whole lot of interesting gameplay either, with the monster encounters spread somewhat thinly. The secret exit is somewhat obvious, but on my first playthrough I somehow managed to lock myself outside of the supply room (and a wall slid up over the window to jump out of to get to the secret exit).
Oh yeah, and as others have mentioned, having bars over a door that open on their own is a huge no-no. Luckily, to paraphrase Flynn Taggart, I'm a compulsive spacebar-pusher.
MAP31: TECHNOLOGY BASE
I liked this map a lot, actually... the monster density is a bit of a slog but most of it is easy-to-mow down zombies and imps. A bit of a switch hunt, but nothing frustrating, and the traps and wall/ceiling opens are inventive enough to keep the player guessing without being annoying... until you try to get to the secret exit. Looking at video runthroughs, apparently it IS possible to access in singleplayer, but you have to make a hard jump off a teleporter... which I somehow managed to lower so that said jump was unreachable. Argh. More noclip. The eastern part of the map (the MP part) is also underwhelming and feels unfinished, as it's just a room full of zombiemen followed by a room full of shotgunners next to a room full of chaingunners. Can't get some variety in here...?
MAP32: THE HIDDEN SLIME FACTORY
Big meh here. As others have said, its overstocked to a crazy extent - soulspheres and megaspheres and blue armor everywhere you turn, and one hallway with something like 20 shotgun boxes in it. Something I'd expect from a Scythe map, not this. There's a few nice architectural points (I'm a sucker for huge changing rooms, the pipes were nice, and there's one spot where it looks like he manually aligned textures to give it a curve). Still, the gameplay was so underwhelming it didn't really excite me. Or I was just bummed after three straight levels of having to noclip to the exit.