Oh boy, I was happy to finally see this challenge going, but boy again, did I underestimate the challenge

I always wanted to do the "simple" structure and now I've got something working. Pseudo 3d like Doom, with a simple level structure. Wall collision is working, a enemy is moving towards the player, but that's it so far. I'm trying to have a little editor, but creating a decent level is tough!

I'm getting old, it took me a while to get the texture alignment working on connected walls. This would have been a 10 minute job a few years ago

Here's how it looks currently (behold my programmer art!)

Keep up the great work!  

Haven't put that much more time in it yet. I'm just implementing features instead of working of a likeable stage

The enemy now has 4 side views which are rotated according to camera. Also added are switch walls, and doors are up next.
The player can now shoot and the shot is also properly handled at walls (and holes in walls, as I allow more than one slice per triangle element)

A bit annoying to have dynamic elements, as all the static content is a huge vertex buffer per texture. The current solution is to manually draw switch walls and doors; which by itself is batched so should be performant enough for a smaller level.