The Scale is as follows:
A+: Cream of the crop. Revolutionary in every way. Game of the year.
A: Very top notch. I had a great experience. Must make my top 10 list to qualify as an A.
A-: Not too shabby. Entertaining and overall good. 90% of the population will enjoy it.
B+ to B-: Still above average. Recommend for people that enjoy the particular genre.
C+ to C-: Average stuff... weak recommendation on my part. Make your own decision.
D+ and below: Crap. Don't go for it, unless it's for a special occasion or something.