Demon of the Well
Gave this a play last night, took somewhere around 2.5 hours (on UV) all told. Got about 80% secrets, and found a ton of different weapons (each number key seemed to have one alternate in it), so I think I experienced most of what it had to offer. Mostly ran pretty well, although I was getting some quite noticeable framerate hits outside of 'Bellagio Gate' (ZDooM/software rendering), and the various visual glitches mentioned in the OP are indeed pretty noticeable, although I suppose there's not a lot to be done about them. The huge final caverns ran pretty smoothly, surprisingly. Overall I'd say it has a lot of the same virtues and a lot of the same faults as the original ZDCMP, so I guess you could say it's certainly faithful to the feel of its predecessor.
The pre-Hell stages of the map were its strongest point, I think. The different aesthetic/construction styles of the various authors meshed fairly well, and the non-linear task/objective progression style made for some legitimately interesting route differences early in the game, mostly a consequence of different ammo counts/weapon loadouts. Hell, on the other hand, didn't seem nearly as cohesive, more like a lot of compartmentalized E3 vignettes sort of smashed together in no particular order. The interconnectivity between different areas remains high, but because the setting is no longer representational in theme and the texture schemes of the different sections differ much more starkly, it seems a lot more artificial/patchwork, somehow. Additionally, by the time you reach Hell you've got most of the weapons (except for that optional alternate BFG thingamabob), and the feeling of sidequest-bound weapon progression was a lot of what made the earlier parts interesting. The boss/finale sequence were at least several steps up from the somewhat anticlimactic ending of the original ZDCMP.
To continue the comparisons to the original, though it's been years since I've played it, I remember that the ammo in that one just sort of dried up about 3/4 of the way in, making the proceedings something of a miserly trek up until the ending. Not so here, there was generally more than enough ammo throughout, probably even too much where the really high-end stuff (read: cells and souls) is concerned--I got the impression that it was assumed the player would just spam the hell out of the Dark Claw to get through the endgame. Really went overboard with the frag grenades as well, they were far more useful against groups of fodder earlier on, but they keep being handed out like candy all the way through to the end. Oddly, it was probably bullets of all things that I was most often low on. New weapons seemed mostly reasonable; I wish the grenades could've been thrown in an arc more effectively, and I didn't make much use of the nailgun (although it was good against those evil Pacman things), but I quite liked both the rifle and the flamethrower. The soul weapons, eh, take or leave. Dark Claw seemed a mite overpowered given its homing capabilities, honestly, at least considering the glut of ammo available for it later on.
Main areas of complaint: Being able to get the computer area map so relatively early on, even if it is only in a secret, feels flat-out wrong somehow. A lot of the appeal of this map is in not knowing what's coming next, and being able to see the whole layout (including 'Hell' being contiguously connected with everything else) spoils a lot, and almost feels more like a punishment than a reward. The cyberdemon junction seems terribly empty given its size....so empty that I had initially feared that some kind of obscure issue in the ZDooM SVN I used was causing a teleportation script or something to malfunction. The low point of the whole thing has got to be the assault on 'Fort Hellpit.' Seems like somebody thought it would be cute to try to create a setpiece aping the gameplay of cover-based military shooters in Doom......it's not. The weird Wolfenstein-esque enemies on the ramparts have a goodly amount of HP, and the height of the ramparts in reference to their hitboxes makes it fairly difficult to get clean hits on them with anything but hitscan weapons, slowing the overall pace of the map to a stultifying crawl. Not cool, not cool at all. Finally, I would recommend putting most of the choice ammo in the big boss battle around the edge of the arena--where it sits currently, it is very easy to pick a lot of it up by accident, especially if enemy AI dictates that you end up needing to use the columns of the Hell Generator to block connection with the boss's BFG 10K-esque attack a lot.
Spoilerific question: Is there some secret way to get that big scary-looking thing under glass in the 'Tech Lab' section, or is it just for show?