I can still make out most of the parts - I think I've been collecting junk for terrain for too long; I can't un-train my eyes.
You're quite right to think, though, that you're moving in the right direction. There is sensible interplay between the various donor objects - supplemental pieces don't looked haphazardly tacked on and the core structure is more than just junk glued down and painted to fill space. Individual pieces and their respective placement makes sense.
This piece also has more... how to put it...
feeling than the last. Add a dish, for example, to the base of the top piece and it wouldn't look too out of place in an old sci-fi movie - it feels rather like a retro-future deathray or comms tower. While the exact function of the building is a little gray, it still has a plausible one. The last build did, as well, but the tighter execution and vague "theme" of this one makes it feel more like it's meant to be in a given setting (pulp, sci-fi, etc.).
It is, as you said, still rough, but improvement is nothing to scoff at. My suggestion, if you want to really hone your skills, is to get away from recycling found objects for a while. Start designing terrain from the ground up,
then consider whether you have something that might work for the build. It will get you thinking more about what you want to achieve than what can be done to the things you have.
Don't simply try to mask a soda can - design a chem storage/treatment facility, sketch it out, then think about the build. The likelihood that you can and will use that soda can is high, but so is are the odds that the focus will be on a more coherent structure, into which the can is "naturally" incorporated. Masking the parts' sources will become a byproduct of the build, not the goal, which will make the process easier for you and more convincing upon completion.
That, and painting. Seriously, what's with that green?