You based on DelphiDoom, but did you do the Geomipmapping (aka LOD terrain), frustum culling, lightmaps and shadows yourself? It is definitely advanced, the code easily gets twisted and complicated when you want to put all those features in. I didn't have time to implement those things, although shadows and frustum culling is high on the list. Professional graphics too, and you already mentioned that the level design took some time. I can imagine. It runs fairly well on my old P4/NV5900.

And as a bonus, you got me interested in DelphiDoom. These seems to be no Mac support in it? Not even Linux?