Burned wort tastes....well, burnt. Like any other burned sugar. Not very good.
My first decoction mash many years ago, I burnt the decoction mash. (Lesson learned from that: add some water to the thickest 1/3 of the mash after you pull it and before you start to boil it). The burnt flavor carried over into the final beer, which was an Oktoberfest. Oddly enough, the burnt flavor went away after about a year in the bottle,