Sneaking this in before hype for the update (and the update itself) wipes out all other thought -
WIP of the changes to B4, focusing on making last easier for RED to defend:
The stairs leading right in front of RED spawn have been killed. BLU can still get up here, but it'll be harder (either by jumpers or through a choke inside the building). A new smaller set of stairs has been added so RED can still get into their spawn easily, but it makes spawncamping far less useful.
This also has the side effect of weakening this area as a sniper line. Snipers will have to jump down to take effective shots, meaning no easy retreat from BLUs advancing through the mines flank.
The top of the stairs will actually be a potential sentry location, but I don't see it as being a very effective one -- the one across from this stair (behind you from the POV of the photo) should be considerably more potent.
On last, the intended sentry areas have been widened, more ammo packs have been added, and some cover now breaks up the open ground. The second picture (with the dumptruck) shows what I'm intending to be the preferred sentry location on last.
I've also done additional optimization on last (and at BLU's first spawn), but let's face it, screenshots of that would be boring as hell.
B4 won't see a release until I can watch more data/demos from B3, but then I also have to create a better finale. That'll be quite a lot of work by itself.