Your improving in leaps and bounds veggie

The central tower thing, needs more sides. I'd suggest maxing it to 12 sides. In the same area, terrain the floor (as you know :p) and i'd suggest a different texture.
in the green corridor, with the pipes on the ceiling. click on your pipes, and have them droop a bit in between brackets (pull up the vertext editor). Also do each of the 5 pipes seperately to make each pipe have a different droop, and then clone them to the rest of the brackets.
In the alien base, the shelves with boxes on them look too uniform, twist them a bit, and add some smaller boxes.
In both bases, the walls need to be jazzed up a bit, to stop them looking flat (BECAUSE WALLS ARE NOT FLAT) and boring. Just add some columns and butresses etc. Or add some protrusions.
in the hummy base, the pipes texture doesnt look too good.
Also for the tower, it looks like it needs something on the top.
A massive improvement on the last one though! GJ!