I rate restaurants on four criteria: food, service, ambiance, and value. The lowest possible rating is one-half of a chili pepper; the highest possible rating is five chili peppers.
Ratings are, unavoidably, subjective. Maybe a roach crawling across my taco will produce a half-chili-pepper rating for food, but so far I haven't had to confront that possibility (for which I'm grateful). Five chili peppers means everything was absolutely perfect, which doesn't happen too often either. If something's just OK, that's two and a half peppers. Otherwise, the ratings go up or down in half-pepper increments as the mood takes me. If you don't like that, write your own damn blog.
Service ratings encompass the restaurant's floor staff and, indirectly, the kitchen staff. On rare occasions when the kitchen staff intrudes on the dining experience sufficient to be evaluated directly, it generally does not bode well for the establishment. There may be exceptions, as when a restaurant is designed so the kitchen is part of the dining area (see, for example, Dough Pizzeria Napoletana), but generally speaking, where there's a wall, they belong on the other side of it. Evaluation of the service rating starts when I arrive at a restaurant, and ends only when I'm gone. And mistakes can happen; not all of them justify lowering the rating, although if a number of trivial little things happen, it can start to diminish the dining experience, and that's when pieces of a chili pepper will go missing. Two and a half chili peppers means things went OK. Three is good, but just good.
Ambiance takes in everything about the physical and metaphysical restaurant: the look, the feel, the noise level, the furnishings, the smells, the table settings, the floors, the decorations on the wall and on the table. I think it's obvious that a mom-and-pop taquería gets judged on a somewhat different standard than a fine continental bistro with dressed-up waiters and wine lists and all. If you think they should be judged on exactly the same standard, you need to explain yourself to me.
Value is also subjective. If I pay about what I'd expect for food of the calibre I've just eaten, that's two and a half chili peppers. Better food at the same prices translates into better value. More food at the same price may or may not. This rating comes down to whether I feel cheated when I leave, and how strong that feeling is.
Questions? Ask.