I truely support your effort to a better graphic.
I'm an oldgamer, not that I'm old but I love to play old games: I love the era when the actual contents were more intriguing, thought provoking, full of experimental challenges (of game makers) and when those were not be concealed by outer materials, such as graphics. So it might be not logical for me to eager for a better graphic of this game.
However, for some reasons the graphic of this game is actually quite bad that it sores my eyes sometimes. For me, the mixture of 2D and 3D is OK. But the main problem I think is that the makers didn't distinguish the texture of the walls and the floors appropriately so it gets me really confused even unconsciously. The finest example might be the level 1-1. We all know that there is a small path to the hidden druid temple, and the texture of wall and the floor is so much similar that it just looks like a bunch of greens and browns - seems like someone has puked on it all over.
The second problem I think can be solved by your project - the graphic gets even worse when there is not enough light. This is why I always cast glow even when I'm outside a dungeon. I used to watch my magic map rather than the actual game screen when it's dark and I couldn't cast glow, and later I figured out that it was because of this phenomenon.
I just guess (since I don't know that much about anything) that the first problem should be solved on its own way, but of course could be subdued by upgrading the graphics overall. I really cannot remember if Hexen had the similar problems because I had played it relatively long time ago.
Anyway I think what you're doing is wonderful. Just my two cents on it
