What do the ratings mean?

At the end of each post, I give the pizza a letter grade, from A+ to F. So what do those mean?
Well, not much, frankly. My main intent in each post is to describe the pizza, not to judge it. Since opinions about pizza differ so much, whether I like it isn't necessarily going to be that helpful to you, unless you and I have the same likes and dislikes, which is unlikely.
I try not to let my prejudices and preconceptions get in the way, but there's no getting around the fact that for me, the ideal pizza has a thin crust, as well as certain other attributes, and I'm not sure that any pizza without those characteristics could ever rate an A+ from me. But that's why I always try to describe, as objectively as I can, the appearance, texture and flavor of the crust, cheese, and other components of the pizza, so that even if I didn't care for it, you can decide for yourself whether it sounds like a pizza you might like to try.
For the same reason, I try to stay away from purely subjective terminology. I may say that a crust was soggy, or that the sauce was salty or the cheese was burnt, but never simply that the pizza "sucked."
Having said all that, I know that inevitably my subjective reactions are going to creep in anyway, and I figure, as long as I'm at it, I may as well throw in a rating at the end. I try to stay fairly consistent by checking how I've rated other pizzas, so that one place doesn't end up with a higher or lower rating based simply on what mood I was in or how hungry I was at the time, but it's an imprecise system at best.
Another variable, of course, is the time and day when I visit. Maybe I got a slice that had been sitting out for a half hour, and had I arrived five minutes later, I could've gotten one fresh out of the oven. Or maybe the Wednesday lunchtime employee isn't as skilled a pizzaiolo as the Saturday night person. But that's the pizzeria's problem, not mine; if a chain is only as strong as its weakest link, then a pizzeria is only as good as its worst pizza.
I'm probably a little bit of a harsh grader, compared to most people. To some people, "C" sounds like a bad grade, but to me, "C" means average. Not bad, just average. If you need a pizza fix, it'll do.
"B" is a cut above average. Among the better pizza places around. Worth driving a little out of your way, or spending a little bit more for.
"A" is truly great. Among the best pizza in the area.
"A+" is reserved for world-class pizza, the kind you'll remember all your life, on a par with my all-time favorite, Patsy's in New York City. I may never find an A+ pizza around here, though I hope I do.
"D" is good enough to eat, but only if you've already spent the money on it. F is not worth eating even if you've already paid for it.
The bottom line, then, is that the grades are rough guides to my overall impressions of a pizza at the particular time when I tried it, based on its objective characteristics and my subjective preferences. No more, no less. So if I give your favorite pizza a lower grade than you think it deserves, by all means voice your opinion in the comments section, but don't get your blood pressure up over it.