The bases:
The main problem was BLU's (and advertantly RED's) cap zone is easily locked down by 2 sentry's; God forbid if there were ever any more since most server settings allow 4 engineers. The problem wasn't the concentration of sentries but their dispersed positions. Taking out one sentry usually allowed enough time for freshly spawned players to see the action and immediately defend that flank before any real damage (and a capture) is made. A direct result of hte 3 catwalks. Destroying one position meant crossing the yard to take out another, then moving further again to take out the third etc.
The cap room itself is of a reasonable size, but having the catwalk around it means that sentry's can defend from up to 3 seperate high ground locations, that even the most skilled of executed ubers would struggle to take out more than 1 nest.
The 2 caps that were achieved were ninja caps at that, performed by a scout coming from under the one RED sentry position, and dying on the point, and a dead ringer spy whom zapped the sentry, picked up the dropped intel, moved it forwards, died by my hands before immediately uncloaking picking it up again and capping it before dying by the unzapped sentry. (Well played by the spy, these are usually my moves, but ninja cap none the less given the cirumstances).
I almost did the same thing as scout on RED but died
on the hazard strips from the 2 BLU sentry nests. (QQ)
The yard has too much high ground overlooking it. You should consider removing the battlement's entrance to the yard, moving its path to the small ramp room beside it, and removing the catwalk that was behind it. Having 3 entrances and a secondary 4th accessible by soldiers and demo's only diluted player efforts and confused players assaulting, particularly when dealing with all the static defenses dispersed throughout the base.
See:
Additionally, the right spawn exit that leads to the drop down. Remove the balcony and replace it with windows that cannot be shot out of (to balance the SG issue, and any snipers that prefer to sit outside of their spawn). This should still allow players to see and acknowledge their cap zone (through the glass) and any immediate threats in the yard after a respawn.
When compromising this particular piece of advice, to what ever work around you do execute for this location, bare in mind that spies should always be able to zap a teleporter entrance.
The no mans land:
The middle was rather long, and by long i mean looooong. Either cut out a chunk of the length or add in more buildings. Whilst the area was wide and generally open, a sentry (with support) could lock down one flank from inside or behind the forward hut, whilst soldiers, demos and snipers had the high ground in the very middle, with the medium health. Making it very difficult to assault beyond your own bases walls.
Either cut out a portion of the length:
Or add in a lot more buildings on the flanks:
Or maybe a combination of both.