I'm going to bump this thread, as it's the latest discussion I could find on this subject (forgive me if I missed a more recent one).
I'm halfway through a recent megawad in Hurt Me Plenty, and at this point, every map appears to have at least 300 monsters in it. Now, each level goes on and on and on... endless traps, endless Revenant shrieks, endless Arch-Vile flames on my face. Endless armies to battle. Some maps begin in a small hallway and turn out to be these huge places. Other begin in an already giant courtyard. I find it so tiresome.
A few (only a few) of my favorite WADs I've played over the years feature some really large maps. That isn't why I enjoy them, but I don't mind too much, as I find their other qualities more than compensate for that fact. Also, I've grown accustomed to them, so I can happily play them again and let a sense of familiarity, along with their other good qualities, carry me through. However, I now feel I can't really enjoy any new WADs that are epic in size. They're nicely made, for sure, and good-looking, but they're just exhausting. I don't have the inclination to put in the time and effort in exploring them to the extent they demand from me.
For me, the ideal Doom map isn't a sprawling epic. It's a 20 or 30-minute action scene that stops when you press exit, and then I can imagine the Doom guy traversing the base, or whatever, for a couple of hours without incident, until the next level, another 20 or 30-minute action scene. I'm not rigid about this; I can certainly tolerate longer maps, but not too long, and not too many in a row.
I recently played SIGIL II, which I loved, and the maps were very pleasant in length. The longest one, Descent into Terror, was still like a hundred monsters, and while longer than previous maps, it was not excessively so for my taste. Also, I could roll along with its length knowing that it was the last map before the boss level. Furthermore, while occurring in a large, open area, it was not confusing to navigate, and was linear to play. I find that large, non-linear maps make me anxious.
All of this ties into my preference for Doom 1 maps over Doom 2 maps. I prefer shorter maps. I don't need massive, epic battles that never end, and in fact, I don't need no ear-raping armies of Revenants, and Arch-Viles reviving monsters all over the place. I just want a sustained, moderately-sized "action scene" in a moderately-sized area, for half an hour, and I'm good.