One of the biggest talents Heinlein had was his ability to be evocative rather than descriptive. Heinlein’s characters and worlds were always very vivid to me, yet he didn’t spend a lot of time on long, descriptive passages. The details just sort of popped out of the dialog or in the small amount of describing he actually did.
Heinlein is the anti-Brett Easton Ellis. Writers like Ellis will spend pages describing in minute detail a character’s clothes, his watch, shoes, the trade names of the materials used to make the fabric on the guy’s freaking sofa, etc. Some people really like that level of detail.
Heinlein would go into detail, but it was usually about technical subjects. In terms of characters and background, his exposition was there but buried in the plot and dialog most of the time. So I’d read a book and realize that I could picture all the characters in my head, the planets, the spaceships, or even the entire culture, and not remember actually having them described to me.
Perhaps it’s because Heinlein worked in archetypes and drew on familiar culture and shared experiences, so the (North American) reader could easily place himself or herself in the story. But however he did it, Heinlein’s backgrounds and characters always just leaped off the page for me, and it made his books much more compelling than most other SF, or other literature in general.
At least, that’s what it did to me. Maybe Heinlein is polarizing because people who don’t share the background don’t feel the immersion and the books don’t have quite the same impact.