Doom: The Lost Episode

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though a few in particular are heavily modified for purposes of gameplay or aesthetics

A bold choice, not a very good one either.

The first map is clearly made of some recognizable Doom beta stuff (looks like maybe 0.4? Dunno been a while) but the "liberties" taken are absurd, this set wins the award for some of the worst visuals I have seen outside of Maximum Doom, some of the original Playstation exclusives have been, for lack of a better term, tampered with and odd little things have been added to them that stick out like a dildo on a windscreen for how horrendous they look.

This is sort of the official (but not really) extra/unused levels but with generally superfluous additions and terrible retexturing, 2 stars.

M1 a little confusing but great visuals. M2 was easy and ugly. M3 revenants...
M4 soo much detail, love that train. M5 a psx map already played and one I didn't like.

M6 a psx map already played but I like. M7 pain elementals how I love them.
M8 that archvile doesn't belong here. M9 already played.

You don't need d2 stuff to make good gameplay in doom. And there's a lot of inconsistency in the visual deparment. 
 

This is okay.  Some unused beta content, lotta console content.  I can appreciate the increased difficulty, but some of the texture and music choices early-on kinda put me off.  Didn't much care for E5M4.

It's not terrible, but it isn't hard to see why the beta maps were scrapped from the final version of the game.  Give it a try, if you're feeling bold.