Somewhat lesser-known sci-fi novels I read in the past:

The Unincorporated Man (and three sequels)

Cross between science fiction and fantasy: Harry Potter and the Methods of Rationality ("HPMOR") - the premise is that Harry Potter is raised by a good aunt and uncle, and is taught the Scientific Method and so he uses that when encountering magic.

Old Man's War (and sequels) by John Scalzi

Redshirts by John Scalzi

Science-reality: Surely You're Joking, Mr. Feynman!

Ra by qntm

There is no Antiemetics Division by qntm