Loved it, still think about it months or years later. I never read books a second time, so for me that's not a qualifier for 5 stars.

Just an excellent book, but with minor flaws. Usually related to pacing.

Just decent, was worth my time.

Obvious issues with the plot, writing, characters etc. For example if your characters are cardboard cutouts you end up here.

Never rated a book a 1. I don't rate DNFs, and apart from that I'm pretty strict in my book selection.