"Tunnel in the Sky" impressed me with various characters and portrayals, especially given it was written in 1955. On the other hand, I felt that "Farnham's Freehold," given situations and certain characters, left more questions than answers...especially in regards to plot thingys.
I am still looking to read Heinlein's "Variable Star" (which I attained in a surprising manner) as well as some other books and short story collections. And, I may read "The Door Through Summer Again"...someday...since I'm in a conundrum of what to actually read next.
He--Heinlein--seems to have a certain curious
theme, which I've noticed other readers of Heinlein have caught.