A grading system?

After a weekend in Richmond, I am ready to start considering my first additions to my posts. But first, I was thinking of what grading system I should use...
Just considering a few options:
The vaunted Michelin system seems a bit sparse. The NYTimes has a slightly less sparse rating - 1 star is good and goes up to 4 stars. The WaPo critic favors the 4 star approach while considering 1/2 stars in between. So, using this system, that would be a total of 8 grades (or 9 possibly if one can "award" a 0 star) between a satisfactory (1 star) to excellent (4 stars).

I think I'll just stick to my roots in the stuffy halls of academia and award anywhere from a C to an A (with the pluses and minuses). Thats a total of 9 grades. An F would indicate a terrible dining experience.
So here goes:
F: Poor; avoid
C- to C+ : Varying degrees of satisfactory
B- to B+ : Varying degrees of good. B+ would be very good.
A- to A+ : Varying degrees of excellent.

I fear I might be giving out a lot of Cs.
To calibrate from some DC experiences: The earlier mentioned chain Lebanese Taverna would garner a C+. 2 Amy's (B), Zaytinya, Galileo (B+), Komi (A-) (tending to an A) and Cityzen (A-).
Obviously, this system is fraught with errors: The glaring - if made only after a single visit (could have been an off or on night. Maybe I ordered badly (thats happened many times !!)). What about creativity and presentation as a supplement to actual taste?
What about ambience, interiors and service (this is a BIG one. Shoddy to snooty service have ruined more than a few terrific tasting meals)? Should the rating reflect the food or the overall experience? And finally the price. Is there a snobbery or other "premium" when the creations dont really warrant this?

I guess I'll stick to an overall impression of the place (based entirely on my and/or my dining companion(s) thoughts). Perhaps some factors trump others. In any event, one factor would indicate this worth visiting more than once. Right?
More as I proceed.