Gave it a try, here's my thoughts.
First off, it kinda just looks like you copy/pasted the levels straight out of the iwad and placed them onto the map. While not the worst approach, the idgames archives doesn't really approve of that sorta thing, and I think would've been a better idea to merge them all together instead of stringing them sequentially. I also was able to skip about 80% of the FreeDoom Phase 1 segment, seeing as you decided to start that where one of the secret outdoor areas from Doom 2 ended. I'm not really sure what you were trying to do there.
Secondly, you seem rather new to this whole mapmaking thing, given the stuff you made to connect levels seems rather simplistic and orthogonal, as well as the fact that I can tell that you just used the LITE texture as a default texture when you weren't able to find a good replacement for them, most evident in the FreeDoom Phase 1 segment. Were you only using Ultimate Doom Builder as an editor?
Aside from that, there really isn't much else to say about this map, as although it's a novel idea, I don't feel you've got the chops to really pull such a thing yet. Combining Iwad maps into a standalone level is kind of a tall order, and you'd probably be better off trying to figure out the ropes though a standalone level. What I can and will say to you
: Take a look at this,
, keep trying, and always make sure you have a good idea of level progression.