It might be a nice end of year stat that Storygraph could generate:

• The book you rated the most above the average
• The book you rated the most below the average

eg, a book that's averaging 2.8 stars and you gave it a 4.5. A book that was 4.1 stars that you gave 1.5 stars.

Don't know if you need to tweak that one though because books with only one or two ratings might swing wildly and be less interesting than even books with just 50 ratings, or enough to even out a bit.