MAP26 - BETWEEN SCATTERED CORPSES
I actually liked this map, because if there's one thing I love about Doom that has become lost in current-gen FPSs, it's monster infighting. This map tons of it - obviously required at the start with the Spider Masterminds, but also doable throughout with the monsters teleporting into the main area. There was also some good use of Arch-Viles. The room with the three barons at the bottom of the stairs was a lame end, though - I would've ended it after the AV/demon corpse room.
MAP27 - FORT HADES
At first I thought this was going to be a good KDITD-styled techbase map, but a strong start falls apart near the end. Requiring the player to shoot a wall to proceed is just silly - yes, it has a different wall texture, but it's not very obvious, and it's easy for the player to go up and spacebar it to no avail. I ended up hitting it by mistake due to a wandering lost soul... "blow up the wall with a crack on it" was a popular thing in Duke Nukem 3D though, so maybe it's just something lost in time. I also really hated the Megasphere secret (being teleported into a slime-floored area while monsters shoot me in total darkness? Sure!)
MAP28 - CITY OF THE UNAVENGED
Very nice city-type level. The buildings are unique-looking enough that one doesn't get lost, although it is a very tough switch-hunt. I actually like switch-hunts, though it can get frustrating if some parts are too obscure. I did get stuck for awhile at two areas - one near the upper right of the map where you have to jump across a gap, and then opening the bars in front of the yellow key door. The blue key was kinda wasted (as the key is right next to the switch, which doesn't seem to do anything that couldn't be done without it) so using the blue key for another switch indicator down the line would've been a better choice. The yellow key area also felt tacked-on as opposed to the rest of the very cohesive map. The fights are nice and challenging, with excellent AV use and some nice surprise Cyberdemon placements. Fun map, though switch-hunts aren't for everyone.
MAP29 - ISLAND OF DEATH
What a mess. I got through this with only 17% kills - grabbed the red key at the start, through the door, found the pentagram/second red key area (though the gap in the wall is very well hidden), into the red door, hit the button for the lift, walk past the pentagram teleporter into the exit. Uh, okay. Clearly there was a lot more to the level (and two red keys?), but damned if I felt like bothering to find it.