I'm playing through City of Pandemonium right now and since it was called out as not looking like a hell level, I thought I'd offer my own thoughts.
First of all, I definitely see how the mapper intended to make it properly infernal, but I can also see how someone would have their sense of verisimilitude disrupted by it. I think that, like map22 with its green slime, it comes down to a few texture choices that disrupt a generally cohesive design.
The biggest offenders, I think, are the 'exterior window' texture and the brown/gray/black building texture, both of which are too strongly associated with stuff like city levels or generic Plutonia designs to not clash with a proper fleshy red Doom hell. I get that you were probably going for a crowded hive look with the exterior windows, but it feel flat for me in practice. The panel and stucco textures might also be overdoing it in a few areas. That said, I don't think the most basic brown stone and rock textures are necessarily a problem for the infernal look, just the neater, more 'human' ones. I'm not sure what you would replace them with without using custom textures, though, even assuming you wanted to replace them in the first place.
The good: the use of flesh/stone/blood textures, especially where the architecture has been eroded or cracked to show the gory 'mortar' beneath, is excellent and perfectly appropriate for the hellish city. Fire and lava are also well used as decoration--I especially liked the freestanding 'ovens' for lack of a better term with fire visible at their bases. The dock area was cool.
Finally, for context, it might be worth saying that nonlinear city-type levels with 'streets' and freestanding buildings often annoy the heck out of me, and the ones in this megawad have generally been pretty good despite that... Sorry if this sounds like damning with faint praise!
I just played Forbidden Archives so I thought I'd offer my feedback on that too.
I agree once again that aspects of it don't really seem to fit into Hell. From a design point of view, I think that the problem is that, while a labyrinthine library of forbidden knowledge is bang-on in terms of infernal flavor, Doom 2's bookshelf texture and the texturesets it's visually a part of are equally if not more strongly associated with human cities and generic Plutonia looks (again). So you need to do some extra work to convince the observer that it's a library in Hell. Right now nearly the only thing doing this is the marble faces and gargoyle switch textures. Some more blood, flesh and fire, evil symbols (on the walls or on the floor), some dark ritual sites (such as altars or the aforementioned symbols), all could go a long way towards fixing it up.
Oh, and lose the blue. All the blue water should go, in my opinion, and be replaced with blood or lava, or maybe a non-liquid texture like snakes, ash, embers, or bone. In the first outdoor area, a red or black floor where you've got water would look right at home with the brown-and-yellow crackle. The blue carpets inside could maybe stay once enough hellish greebles have been added, I'd have to see the result to decide.
Oh, and since I'm making so many suggestions, I want to be clear that I'm offering these ideas in all humility. You're obviously a great mapper, the levels are all very technically amazing already, and you've obviously done enough work on them already that I wouldn't expect you to make large changes based on anybody's opinion, let alone a relative nobody like me. However, the aesthetics of various styles of Hell or Hell-corrupted maps are such an interest of mine that I can't resist analyzing them. :)
Last edited by jerrysheppy on 05-26-13 at 05:04