HFCS is corn syrup that is higher in fructose than regular corn syrup. Fructose is “fruit sugar”, and a very simple one at that. (Simple has nothing to do with ignorance; it has to do with how far it has to be broken down before it becomes glucose.) It’s not going to hurt you, I promise.
It has very little flavor. The different percentages of fructose in the different corn syrups make them have different qualities, such as browning or sweetening, in baked goods and soft drinks. Plus, it’s cheaper than sucrose because you can make it out of corn starch. So, it’s a powerful sweetener, it has no flavor, and it’s cheap. No wonder it’s a star.