Alright, well, I'll try to keep it somewhat brief. No idea if I'll succeed (future me here; I definitely failed at briefness!)
Keep in mind I haven't quite finished the pack yet, so while I see you moving toward some of these ideas as the levels have gone on I don't know if you've already got there without me... so don't be mad at me if you've already figured out a few of these things. That is the sort of thing that tends to happen with good general principles
I tried to pick four things that I think would be most useful for building "good-looking" maps in this game:
First off, the thing I mention to everyone when I play their early levels, because it's by far the most common thing mappers for this game can do better: whenever you can, it's a
very good idea to put doors into square alcoves, similar to what you see in all the stock levels for Descent 1 and 2. The reason is that the doors in this game are flat textures with no depth, and putting them in spots like that removes any frame of reference for that paper-thinness. It tricks the brain into perceiving the shading on the texture as something closer to actual depth. Basically, doing this as much as possible will make your doors look a whole lot better, and it also gives you convenient spaces for those border lights.
Worth mentioning too, that if you ever want to try making maps for Overload, you'll need to do this for every door, no matter what, because of the way that game's doorframes are modeled.
Secondly, for whatever reason Descent's textures don't tend to render very well when they're stretched. Most other games I've tried mapping for can handle this sort of thing much better... but not this one. :-/ It's best to always reset the textures before aligning them, in order to let them tile rather than stretch across sides. If you get seams when trying to align textures this way, it's often possible to cover them up with creative use of secondary textures. Gratings and warning stripes are especially good for doing that. And because it does sometimes make aligning textures a pain, it's a good idea to build your geometry with some of those those secondary texture placements already in mind.
When push comes to shove, it usually still looks better in this game to have a visible seam between tiling textures than to have anything stretch. Most of the "professionally" made maps that have been built for D1 and D2 haven't got any stretched textures at all.
Thirdly, because most of the textures in this game are designed to represent rock walls, it can be jarring to have too many different colours within one room or area. It's usually a good idea to pick one or two colour schemes and stick with textures using those colours through at least the majority of a map. Surprise splashes of colour work best when they're treated like surprises, and colour transitions work best when they're separated by either a door or a secondary texture. When it comes to texturing maps in this game, what you don't use is
far more important than what you do, and if you can figure out how to choose what you want a map to look like and excise any textures that don't serve that look, you'll be well on your way to making levels that feel professional.
Finally, the hostage placements don't snap to "floor" automatically (because the game's engine has no way of knowing where "floor" is), whenever you place them you have to manually move them down a few units in order to not have them floating in the middle of a cube.
