So, playing through a few of the maps, my thoughts...
Map 3: Comm Center - Pretty solid map! Had just barely enough ammo to make it through on UV. The start would probably be a bit too nasty for anyone who doesn't discover the secret, though. Only other qualm is that the doors have the "panel" bit of the graphic at the very bottom, which looks strange given that those door textures usually place the "panel" at roughly the middle.
Map 4: Exit Planet Dust - Another good map! However, there's a bit of oddity with hidden monsters. The area where the pain elemental pops in behind you has a graphical glitch where the false wall is, and past the drop and brief acid pit, the revenants hidden in the walls can end up firing at you before being warped out of their hidey-holes. One in the open area seemed stuck in his hidey-hole, and never could find an angle to shoot out of either.
Map 8: Traps and Tricks - There's two places with glaring hall-of-mirror effects—the column that lowers to reveal a pain elemental at the start of the map, and the area with the arch-vile past the rocket launcher. And a small nitpick, but with the second set of pick-the-right-teleporters, I feel it would be nicer if the teleporters were more neatly laid-out just to make it easier for the player to remember which one they picked. But all in all, good map!
Map 9: Akuji Blood Pit - This was the first map I didn't really care much for, and the use of a music track from a Plutonia MIDI pack quite handily foreshadows why. It's the first map that really feels like it overuses revenants, with encounters that consists largely of mass revenant waves. But even those, like most of the map's fighting, is easily overcome at range and/or via choke-points with the abundance of rockets the map gives you. The level design is nice, but I just didn't vibe with the gameplay.
I'll go through more later; judging by the number of enemies, Map 10 will be a fair bit longer than these maps.