Not the opposite of fun...

What’s the most serious book you’ve read recently?

Hmmm. If by serious you mean the opposite of fun or funny then I would probably put Children and Grief: When a Parent Dies right at the top of the list, but it was by no means hard to get through. It was accessibly written and kept me interested in a subject one could expect to be hard to take. If by serious you mean really difficult, then I guess I might put Basic Neurochemistry or Principles of Neural Science on the list. They deal with difficult topics and, in some sections at least, nothing about the writing made it any easier. I had to read and re-read some sections five and six times. In the land of fiction I would call both of the Damon Galgut novels I read - The Imposter and The Good Doctor - serious fiction, and the same with William Maxwell's So Long, See You Tomorrow, and Children of the Arbat, and Deirdre Madden's beautiful One by One in the Darkness, though they were all a pleasure to read. Herman Hesse's Beneath the Wheel, William Trevor's Fools of Fortune, and Bernard MacLaverty's Cal are tragedies, though they are not dour books. Or books like Don Delillo's White Noise, A. S. Byatt's The Children's Book or Dickens's Bleak House are serious in the sense that they a not frivolous. They examine serious ideas, and/or have many story lines and characters, and reading them requires some work. You can't dance merrily through them, but I enjoyed them nonetheless. I guess much of my reading could be considered serious but I don't think of reading them as the opposite of fun.