I realized I never defined the scale I'm using to rate these Doom levels. It's pretty similar to the Star Wars one, I'd say.
Things I look at:
1. Fun: Obviously the most important, regardless of whether it's easy or hard, gimmicky or slaughtery, it should be fun to play.
2. Creativity: It's impressive how much weird stuff you can do with the Doom engine, and people are still finding newish gimmicks 30 years after release.
3. Aesthetics: Did you arrange the textures good?
4. Bugginess: If I cannot beat your level because the floor is broken, it's an autofail. If it's only a minor graphic glitch, I'll mostly overlook it.
The usual 0-6 scale applies:
0: Unplayably bad. Either horrendously buggy, or unfun and poor in the other areas with minor bugs.
1: Regular bad. Not fun, but at least mostly works.
2: Meh. Not worth downloading on your 56k modem, but probably worth borrowing on a floppy from a friend.
3: Minimal acceptable Doom level. Nothing crazy, but all the parts fit together correctly.
4: Actually good Doom level. Either an okay level bolstered by some cool gimmicks/aesthetics, or a well executed vanilla level.
5: Great Doom level. Not only fun and well tuned, but also makes good use of gimmicks/aesthetics.
6: Somehow, you made Doom fully 3d or something. I dunno, I guess we can give Hangar a 6/5.
Vaguely attempting to rate all the episodes from before I started doing scores.
KDitD: 4, and it's getting half a point for historical significance.
TSoH: 4, and I mean it this time.
Inferno: 5, best level set in id Doom.
TFC: 3.9? The line between this and Ep 2 is the exact line between a 3 and a 4.
Sigil 1: 3, maybe 4? You have some really strong levels balanced by some pretty poor ones.
Sigil 2: 3ish Same, actually.
Doom 2: Overall, 3. There's a lot of 2s, one or two 1s, but a couple 5s to balance them out.
Master Levels: Rounds up to 2 if I did the math right.
I think Evilution is averaging around 1.5 right now, but I haven't spreadsheeted it yet.