As many others in this thread, i have to say i had a lot of fun playing through this wad. I liked the alpha a lot, and the final version is even better. This is really the wad type for me, because the themes and styles i enjoy most in doom are those of the original games.
Episode 1, as expected, isn't very memorable after only one playthrough, but that is probably due to it's theme being less exciting than the later ones. The boss level, of course, stands out, although i still think i liked that one old e1m8 candidate that never made it into any version of the wad a bit more... the one that had a remix of e1m8's music, you went through some tight corridors, than got teleported to a more hellified version, than went through a big computer hall and fought like four barons in a burning star shaped room.
The other level that i remember is e1m4, but that is because i spent a lot of time in it hunting all the secrets, mistakingly thinking i was in e1m3 for some reason. When i realised my mistake i had to make a pistol-start detour into e1m9, which was also pretty good.
Episode 2 had many good moments, and overall just starting from e2m1 to the very end of the wad i was regularly surprised by many simple, yet awesome design ideas here and there, ranging from a room to a concept of the whole level.
I liked the slightly different direction that ep2 took, even though one could argue it wasn't TOO doomish.
With this direction it kinda felt like ep2 had more thought put into it than any episode from the original, the levels were more specific etc.etc. Not generic enough in other words. :D But i only see this now, and it isn't a bad thing anyway.
Though i kinda miss that one level from the alpha that had all those fake secret doors that opened and only had walls behind them. And the e2m2 from the alpha, the cooling towers. I guess the alpha is good to have around alongside the final release for some of it's levels too. Too bad there are repeats between them, but what can you do.
Episode three too felt well-realised, i especially liked e3m2 and e3m7, though i was a bit annoyed about having to play e3m4 and e3m6 AGAIN, because i had enough of both of them (i think i played through them when they were released separately and in the alpha for a second time. And both were slightly annoying by themselves already).
Overall even if i don't remember ALL the levels distinctly like i do the originals, that will certainly change if (when, rather) i play through this again. Though there was enough memorable stuff as it is, and on the whole the wad was very fun. The only criticism i can even think of that i share with other people (i think like one person said this in the thread) is that there are perhaps too many overly dark areas. But then again, maybe there aren't many more than in the original and i'm just used to brighter levels. It didn't hinder my enjoyment of the wad anyways.
P.S. I should be in the credits :D, i still remember a post in the development thread by hellbent where he said that he was inspired by some thread i had made and he kinda rejuvenated the project after that. That thread was probably dumb, but who knows, maybe without it this project would not have been rejuvenated at that point and would fade into oblivion? =0