This is what I think the numbers 1 thru 10 represent when rating maps.
10. Perfect
09. Excellent
08. Very Good
07. Good
06. Decent (above average)
05. Average
04. Below average
03 Poor
02. Terrible
01. Unplayable
That would mean a map with a rating of 7 would be a good map (good gameplay, good construction, good A.I.). Does this scheme sound reasonable?
You also forgot "0", but I usually reserve that for things that are beyond crappy.