High-end office builds are also efficient rectangular prisms far more often than not, yet they don't feel like hospitals, schools or prisons.
I've spent extensive time in all of these except prisons, and I can tell you the difference is stark. What explains that? Is it all just down to expensive trim and interior decor? I'm sure that plays a part, but that was never my main impression. Instead, it comes down to the layout and light and feel: it's clear when a building, however regular and rectangular, is designed to support and empower the occupants and when it's designed to control and direct.