It depends person to person.
Some people say 1 is bad, 5 is average, and 10 is great.
I basically rate it as if it were being graded for school and 7.5 being a 75% and average. I very seldom give out anything above a 9.5 sence I have started using this grading system and have so far only rated 4 builds to be 10/10s.