"...got interrupted at 80% completion... "
Exactly! The massing environment is really powerful for modeling, but it behaves inconsistently with the rest of Revit (and sometimes itself), making it very hard for most people to learn. Cutting voids in particular is very problematic and janky - i've seen people just stop trying to learn massing modeling because they inexplicably couldn't get something thing to cut that other thing.
When teaching people how to use the massing environment, I've observed that people who are skilled at making families etc. have a hard time, because they are expecting revit to provide something similar to the tools inside the family environment.
I think the massing editor would also benefit from better tools for making just really simple planar models - points, planes and lines. More feedback about WHY the shape generation failed would be helpful