Whoa, what a level! The color scheme is nothing short of disturbing for some reason, the puzzles are confusing and the green slime working as lava is super innovative. There are a few things though:
- There is no way in hell that anyone's reaching that exit in time on Insane, even with the afterburner. It's gonna be a close call at best but I still foresee a failure like 8 out of 10 times
- The mazelike area near the exit - change the texture to something less risque, the matcen texture should be reserved for matcens proper
- Replace the yellow walls blocking the access to the red key with something less jarring
- While you're at it, why don't you replace the three robotlike color-coded textures with the simpler ones from D1? I'm talking about the colored "rock" textures.
- Reduce the number of different door textures used in the level, stick to one or two at most. The valve-like hatch texture leading to the large chamber is fine to leave in though. On the other hand though this is Vertigo and I think I remember similar things being done there, so guess it's OK
- Replace the monitor that lowers the forcefields that lead to the blue key with a proper switch - puzzles are fine but once you're stuck for 30 minutes trying to figure out just how to get to the blue key, something's wrong
- You've brought in so many D1 textures already, why not swap out some D2 monitors for ones from D1 and use both types concurrently? You'd probably have to replace the frames manually, but you could also use the templates and just restore the other monitors, or replace ones of your choosing manually while using the template for reference
- The wrench symbols on the sides of the reactor pit? Nah, something else would probably be better.
- Last but not least, since you're using the lab textures quite a lot, why not use some decoration textures from D1 here and there too?