Looks like quite a nice map from what I've seen of it so far, my only real complaint being that the large open spaces would have almost certainly been cut down or compartmentalized with solid walls somehow, if this were an id map. In yours, it's drawn particular attention to by the presence of lots of 2-sided lines that function as detail in areas that are huge enough to already have lots of sidedefs onscreen at once. It's not an inherently bad thing in and of itself, but it's unfortunately rather inauthentic.
Keep in mind that the original Doom 0.99 release had a low enough segs limit that running out to the far edge of E1M8's courtyard after the walls came down was enough to cause a HOM.
Even after those limits were raised for Doom 2, slowdown was still an issue for larger scenes in 1993/1994, which led to the rearrangement and restructuring of at least one of Doom 2's city maps in order to incorporate more solid blocking walls and limit line of sight.
Damn fine map! One of my favorites, for sure -- it's nice and open, but the cave-like setting gives it a serious sense of identity that copies none of the original maps, while still providing a Mt. Erebus-style layout that kicks some serious rear.
I'd revise the current secret exit location to teleport to a hidden room with the exit in it (E2M5-style), since I was never a fan of E3M6's unmarkedness in the secret exit department, but otherwise, this map is superb.