Doom 2 "Episode 2"

 After a slow start, the final two levels of the first segment of Doom 2 pick things up. The start of the next one "Tricks and Traps" adds the BFG to your armory and throws the first Cyberdemon of the game at you. I've mentioned my love of gimmick levels before, and your feelings on them will pretty much dictate your opinion on T&T. It opens in the middle of an octagon, with most of the doors leading to some kind of gimmick (Brons infighting the Cyberdemon, teleporting Imps, vertically challenged Demons, a "bait" sergeant to lure you into a swarm of Cacos, and a close up encounter with a Baron). Each one is relatively easy if you know how to play the gimmick, but overwhelming without. It's very Sandy Petersen. Also the debut of the Pain Elemental. Their only attack is spawning Lost Souls, which is why they stopped counting for kill scores in later patches.

The Pit is also a great level (and has a kind of similar hub and spoke structure, but less contained/puzzly). I think it's the most vertical level in any of iD's Doom sets. Over 205 monsters on Ultra Violence means the Pain Elementals sometimes don't spawn Lost Souls, so that's a plus.

The Refueling Base (I feel like the Episode 1 levels at least sort of looked like their names. Command and Control has lots of computers, Toxin Refinery has a lot of nukeage, etc. The Doom 2 ones feel a lot more tacked on, there's one area with what I guess are fuel tanks, but there's also a warehouse and a creepy demon cave) has the most enemies of any of the iD maps. Its a lot. Ammo is very tight. Pretty good map, would struggle through again.

Circle of Death is a strong contender for my least favorite map in Doom 2. It just feels very busy/clumsy. There's the titular O of Doom in the middle and there's some enemies in it and on it and around it, and they're just all spread out kind of at random in a way that makes them not terribly threatening or fun to fight. You clear it, and you're closing in on half the kill count for the level in a pretty boring way. It's got big ol' John Romero sludge pits everywhere, just to make your life vaguely annoying (but again, not really that dangerous). Then you clear the little fort (with the world's most obvious/pointless secret) and meet the Arch-Vile. New enemy, cool, but not a great intro (needs more room to move around so you can really see what he can do.) A couple ledge runs later and you can clear the very easy red door and grab an invincibility for your requisite John Romero Caco-Swarm (now with Pain Elementals!) it's a lot less scary in Doom 2 than it was in Doom 1. It is the debut of this cool giant skull exit texture at least. (Which apparently is the switch to drop the shield stopping the evacuation of Earth. No one plays these games for the plot.) This brings us to the infamous city levels.

Doom 2 is, in general, more generous with giving you secrets than Doom 1. The different wall textures, etc. are more noticeable, and a lot of them are shootable (allowing you to randomly get them in a firefight). As a trade off, a lot of them are more stingy with loot. Here's your secret, one box of ammo! But there are more of them, so it kind of balances out.