My highest average rated book I’ve read — Ruby for Grief by Michael Burkard at 4.71. (Forgot this book existed so I’m glad you asked this question.)

Lowest average I’ve read — Voltaire and Catherine the Great: Selected Correspondence at 3 stars.

Out of the ones I want to read:

Highest average — Edwin Hubble’s Observational Approach to Cosmology (5 stars but only 2 ratings)

Lowest average — The Better Sort by Henry James at 3.2

(This is out of 470 read / 402 want to read)