I think the upper path needs to still be lowered some more. There's too much of a disconnect between the action above and the action below, and falling off results in a jarring shift in trying to figure out what the new situation is and where the threats are.
Likewise, the fact that there is a single set of stairs (per side) to get up there means that frequent travel between the upper and lower areas doesn't really happen for anyone but soldiers (it's usually not worth it for demos to try it repeatedly). I understand that you want the attackers to have some kind of offensive advantage there to deal with sentry farms and what not, but I think the fact that there was always an engineer building a teleporter exit to the top level of his own base is indicative that game flow wants there to be a more local path up there. Stairs up around the "backside" of that building would make defenders have to choose between shooting at people up top NOW, or taking the time to try to flank, by which time they may have already done their damage and dropped down.
And on the subject of paths up, I think the current large room you have going to the top in the middle rarely sees any action. It's significantly disconnected from the rest of the map. You could probably tighten it up a bit and expose more parts of that path to the middle area.