I played the map 3 times this morning.
At first it felt like the easiest map 'til now, and by far... but it was mostly because I found one secret without searching for it, being at the right place, at the right moment with the right move.
That's why I tried it again two other times (because there is a touch of non-linearity).
It's a bit more difficult without this secret, still very fair !
I'd say the best area regarding fights is the eastern one, I won't change anything there.

The red key area fight : first part : most of the low tiers guys moved towards the central area when the first switch was activated so, no real difficulty to manage them... then the hell nobles don't present any real menace. Second part : the ambush with revenants and chaingunners. Since you can run to the central area it's also quite harmless (maybe close the entrance door to this area then add a switch in one of the closet of the ambush ?)

The yellow key area fight : first part can be cheese by running back (maybe add a blocking teleporting pinkie or two ?), second (revenants and chaingunner) and third (cacos and lost souls) are cool, not hard but cool.
The arachno and pain elementals appearing when yellow key taken are fair (much easier if you get the plasma from the red door before going for the yellow key)

The green key area looks really cool but the fights are the easiest of the map (the first dormant archvile can easily be taken from far away with RL)(maybe making him and his buddy appear from the ground ?) then, in each of my runs, the mancubus, second archvile etc started infighting before I started firing, making this part of the fight pointless.

So, as for the first three maps, I really like the design, textures, atmosphere, though maybe one or two fights need just a tiny bit of steroid (mostly in comparison with previous maps).