I'm switching over from a letter grading scale to the five star scale as used by Goodreads, so I can stop confusing myself and also simplify things.
Here's what the stars mean to me:
Five stars *****: One of the best books I've ever read! Terrific, couldn't put it down
Four stars **** Very good. I really enjoyed it a lot.
Three stars ***: Good... I enjoyed it.
Two stars **: It was okay, didn't love it, but didn't hate it. And there was some stuff that bugged me.
One star *: Would not recommend, poor and lost interest.