Ok I tried this out. The level design is too abstract for my taste in terms of its layout. Outdoor environmental design is decent but the problem is everywhere looks very same-ish which makes it difficult to navigate (i.e, remember where you've been, and where you're supposed to go). Plus there's virtually no shading outdoors, everything's mostly given a uniform dark shade which further adds to the same-ishness. I don't really blame you too much for that, since shading outdoor terrain is difficult, and there's some argument for outdoor areas having a uniform shade. However it might benefit to have some lamp posts set up every now and then to add contrast which would make things look better, and if you add them near points of interest that would make navigation easier.
Another problem is that a LOT of weapon sounds, both for the player and enemies were missing. In fact, now that I think about it, many other sounds were missing. The player's landing sound after a jump, things that the enemies say when they see you or move around, not to mention ambient sounds. Ambiant sounds like wind, water running would really spruce it up. It could also use a few set pieces like activated explosions every now and then.
Now this is partially due to the sound issues I think, but fighting the enemies here weren't half as fun as the original game's enemies. Like I said part of that is due to the lack of sound; they all seemed to have hitscan enemies so I couldn't tell when they were shooting, or even what they were shooting (i.e shotgun, machine gun). As a result, it appeared that they all were the same enemy, even if that wasn't the case. And indeed they looked similar too, but I know there are only so many different looks you can give to 8-bit human soldiers. Another point is that the gameplay didn't seem to flow all that smoothly. The player encounters enemies in a fairly constant stream, with no build up of tension or anything like that, and the same-ishness of the environment doesn't help that, it also doesn't give the player any real sense of progression.
Due to the confusion nature of the level, I wasn't able to finish it. Sorry if I sound really harsh here, I've got the worst cold in the history of mankind and I had a bit of a headache when I played it, which would have tainted my experience of the map, but I think my points are still valid. It's definitely a unique style that isn't done very much in Duke though.
Edit: Also, it appears that the texture that's used for the walls everywhere outdoors has some yellow fullbright pixels in it or something. If you can, I'd suggest removing them. The gloves on the duke weapons look fantastic though.
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