If a different wine is brought to the table that is better than the one you had been drinking until that point, then one says a special berachah, hatov v'hameitiv, meaning, "The one who is good and does good". You also say this on hearing certain kinds of good news.
Say that on Friday night everyone has some kiddush wine. Then, during the meal, you crack open a bottle of something else. With no disrespect to kiddush wine, the other bottle is almost certain to be better and so you would say hatov v'hameitiv. In fact, you say the blessing even if you are not sure that the different wine is superior, so long as it is not actually worse than the first one.
What's more, taste is not the only criterion of better. If the new wine tastes worse, but is healthier, then you still say the berachah. This case actually came up for us during Succot. We opened a bottle of eco-friendly, sulphite-free, beeswax-sealed wine that we had been saving for a special occasion. It was obviously very good for you, but tasted like floor leaner. (Our guests were very kind about it.) But one would probably say hatov v'hameitiv on the stuff, by virtue of its healthiness, even if it followed vintage champagne.