Welcome to Releases!
I enjoyed playing through the levels in this demo - you're using a lot of effects! Some things you can do to make them better, though:
1) Sector brightnesses! Make sure nothing other than light sources is 255. Try making all the levels at least 224 brightness outside and lower brightness inside - no lower than 160 in really narrow and dark spaces.
2) Try merging some of your stair sectors and turning them into slopes! It's pretty easy to make them into slopes - point at a line in 3D mode and use alt+s to slope it! The FOFs might be a bit of a pain, but you'll get the hang of things eventually.
3) Try to do death pit fades when you can - if there are a lot of platforms over a pit it's not necessary because it's a lot of work.