Demon of the Well
Cool, glad to hear it. E2 is actually the part of the BTSX mega-megaWAD that I've been most anticipating, as old shots I've seen from it depict a sort of gothic/stone ruins/catacombs theme, which is right up my alley (although that purple techsky from E3 is also enticing).
I've also tried several of the maps from "Get Out of My Stations" from one of the early betas you posted, and apart from one lone map which didn't feel good somehow, I felt it was generally a lot of fun (I most fondly remember a scenario where arch-viles teleported into a mound of preexisting corpses and started reviving them wholesale). The relative lack of aesthetic variety that I saw didn't seem untoward to me; it was all techbase, yes, but there was a lot of variety within that theme--nukage base, cavern base, base where the real meat of the map is the natural terrain outside of it, etc. The action also seemed pretty varied in pace and style, although none of it was particularly challenging, it did keep my finger on the trigger. I also appreciate the use of revisited 'story maps' to help establish narrative, which is a neat idea that I've only seen a handful of other vanilla-compat WADs use.
Incidentally, I reckon your internal bugtesting has probably already caught this by now, but on map 07, in that setup where you grab a key on an elevated square platform that causes the gate to shut behind you and a spider mastermind to be revealed on the opposite platform, it's possible to grab the key and quickly back out under the gate before it closes. Whether this was an intentional tactical option or not, in the version I played (beta E, I think) it seemed that it was not possible to ever open that gate again. While this doesn't seem to break the map (I haven't managed to do this without actually picking up the key), it does make 100% kills impossible to achieve, since there's that nearby arachnotron closet which only opens when you leap from the platform, and no arch-viles on the map. A small thing, and perhaps not worth the trouble to fix (since a player could still miss those kills even if the gate could be reopened if it never occurs to him/her to leap from the platform), but I figured I'd mention it. Every other technical issue I found (and then some) was already mentioned by others earlier in the thread.
One other thing....you might want to re-alter the palette again. The one from E1 was nice and all, but I think we can all agree it would be even better if it were weighted more towards brown. Sepia-toned, even.