It doesn't feel like Doom though. It's just empty and huge, with scarce items, repetitive layout, no slopes, no switches and extra stuff. Basically what you've got is a noob-style map. Also I didn't find fun trying to defeat several battlelords in an open location without having enough rockets, so I had to cheat on those ones.
A few tips to make a map look and feel more like Doom:
- Use sprites for wall trimwork that is absent from Duke tilesets (same for scenery)
- Shade walls like Doom does (W and E walls are brighter than N and S walls)
- Use lighting effects like random lights, cyclers etc.
- Tune down the visibility fog (it doesn't work right in Duke3D, making everything pitch black in the distance, while Doom has a "torch" effect instead)
- Scale your map accordingly; don't stretch or shrink textures from their normal size
- Align everything to the grid (as Doom didn't have floor/ceiling panning feature)
- Keep the visible wall count small (mind the visplane overflow!)
- Use texture choices that are reminiscent of Doom
- Use masking walls that don't repeat y-wise
- Finish level with a switch, not a nukebutton