Taste is unquestionably an individual affair. Some will rave over the flavor of a Limburger, while others won't touch Brie. But no matter your preference in type of cheese, there are certain factors that always should be taken into account.
First, prepare your senses to make a good judgment. Before smelling or sampling a cheese, try to optimize conditions. Make sure your tongue and nose are ready. How? Avoid smoking for at least an hour before testing. Be a little hungry, but not excessively. Avoid heavy meals before choosing a cheese. Of course, your nose and tongue should be at peak capacity, so avoid making judgments when you're ill.
Second, avoid distractions. No, not the sort caused by noisy traffic, cell phone calls or children running through the store. More subtle ones. Don't use hair spray or strong cologne shortly before picking out a cheese. Avoid other odors such as those from onions, chili or other foods with pungent aromas.
Third, isolate the cheese. Don't try to smell or taste an extra sharp cheddar right next to an Emmentaler. Cheeses absorb odors from anything nearby. A fine cheese shop will help you by keeping strong cheeses separate and well wrapped. Shop accordingly.
Fourth, don't judge all cheeses by the exact same criteria. Certain basic factors should be common. But each cheese type has a distinctive flavor profile, texture and consistency and so on. A semi-soft Muenster won't behave the same as a semi-hard Feta.
In fact, use the individual characteristics as criteria. Each cheese should follow its own standards. A Brie that has become crumbly, quite unlike its gooey nature when young, is signaling deviation from perfection. A Parmesan that is soft has been altered by external conditions, and generally in a way not to its advantage.
As for general criteria, some are obvious.
Every cheese considered should be fresh, in the ordinary sense. 'Fresh' cheese is a category and is one that is aged for a short time and intended to be eaten shortly afterwards. Ricotta is a good example. But even a 12 month old cheddar should not have hard spots or certain molds. In that sense, even a year-old cheese should be fresh.
Some mold, for example in blue-veined cheeses such as a Stilton or Gorgonzola, is deliberately introduced. That's what gives those cheeses their particular identity. In such cases, the veining is the result of the introduction of a certain species of penicillum spore. But others represent simple spoilage.
Other type-specific qualities apply. A Brie should be moist, while you should expect an Italian Grana to be brittle and hard. If the characteristics have been reversed, you know something has affected the cheese in a negative way.
Let your nose and tongue be your guide. After all, the most important criteria of all in judging a cheese is whether you enjoy it!