Ok, I had a long discussion with Con, and we came up with this list:

-replace 4 of the 5 banshees with wasps
-raise the control room to shorten the warthog tunnels
-fix the giant walls so they don't look ugly
-fix all other ugly areas (lol)
-use the terrain on the grassy areas to add cover, instead of using makeshift forerunner stuff

Other stuff TBD. And I have no idea how long that will take.