Demon of the Well
E4M5 -- They Will Repent - 100% Kills / 100% Secrets
My memory of this one was not very clear, which ultimately resulted in my needing to essentially play it twice in the interest of completism--there are several different ways to traverse the layout (indeed, both the blue and yellow keys are optional, although this is barely relevant in the latter case), and if you go a certain way before picking up the blue key, you end up permanently locked out of one part of the level and unable to backtrack. Getting the blue when you have the chance, by contrast, allows you to see the entire level and ultimately enables you to backtrack all the way to the beginning, if you so desire.
In contrast to the strange muddy Legoland look of E4M4, They Will Repent returns to the definitive E4 texture scheme of marble and iron, here arranged as some kind of strange blockhouse full of channels, sluices, and overlooks; the main structural walls are often thin and fairly porous, with most major rooms having several entrances and often a number of viewpoints into adjacent rooms. Oh, and of course, the sluice system itself is full of tainted blood (and lava, deeper in) although the player doesn't usually spend a lot of time sweating the platforming. It's not a bad map, but it's much more interesting as a construct, with its numerous vantage points and multi-terraced arrangement, than as a battle engagement--it's mostly zombiemen, imps, and pinkies who are usually unable to physically reach the player, here. Lost souls, of all things, are actually the enemy MVPs here, since their propensity for silently rising out of the blood channels and their ability to pass through the high windows and other openings between individual rooms allows them to sometimes attack unexpectedly and from strange angles. The BFG secret is kind of clever here, one of the earlier examples of its kind.
E4M6 -- Against Thee Wickedly - 100% Kills / 100% Secrets
Ah, yes, I think that this is one of Romero's most interesting maps in all the DooM series, and apparently lots of other folks agree, as this is probably the most-imitated map from E4, and many maps in well-known WADs that are not otherwise imitations by any stretch contain nods or winks towards it. A marble fortress built in and around a bitter volcanic cyst in the planet's surface, it combines dangerous terrain, some light platforming, non-standard teleporter logic, and a strong enemy presence (including another cyberdemon guardian watching over the exit) into a fairly short but very brisk outing.
I remember thinking this was the most difficult map in the episode (and thus, the game) waaaaaay back when I first played it, not only a function of the monster population, but also of a certain element of environmental attrition. While you can access most of the map from the outset, and characteristic of Romero, many of the rooms have more than one path through which they can be entered/exited, the truth is that the actual thing placement in the map means that there are really only one or two 'correct' itineraries for finishing, and many more that are vastly inferior, most often so because they'll end up requiring more radsuit-less dips into the lava than necessary, partially a function of the quirky central 4-destination teleport design. Indeed, while my combat skills have improved enough in the years since that I'm not particularly threatened by any of the monster encounters here, I ended up taking one of the aforementioned highly inoptimal routes (due again to cloudy memory), and so probably ended up soaking more damage from lava than from all of the monsters combined. Not to downplay the monsters too much, though, as they are an ever-present concern given the generally restricted footing available; I think I've already observed once earlier in an earlier post that cacodemons tend to be used pretty badly in most maps of the original game, but not so here, as their flight ability is put to fine use given the awkward terrain. There is once again an easy way to quell the cyberdemon (assuming you've explored thoroughly) in the form of another V-sphere, but at least he can troll you a bit by knocking you back into the lava and causing you to lose powerup time if you aren't careful.
It's a cool map, fun even if you play it very inelegantly, like I did this time.