I don't know what it is but the flavor is so good to me. I absolutely love mixing this with vodka for a mixed drink, it's one of the ONLY things I will make a mixed drink with. It's got the perfect amount of carbonation and caffeine.
I also love that red bull is so accessible and comes in so many different sizes. I can find it almost anywhere (gas stations, grocery stores, bars, drugstores) and I can get the size that best fits my needs. I cannot stand the sugar free version but love the regular red bull.
I do feel energetic after I drink it, but not to the point of running around. It's more easily described as I'm more alert at work and more productive. I should pitch Amp to my boss and see if he will begin supplying it for me! He does actually currently buy Mountain Dew and keep it in the refrigerator, so Amp is not out of the question (in my opinion).
I typically drink a 16 fl oz can of Amp in about 1 hour or less and the effects last 4+ hours after. I don't feel any crash or anything when it's wearing down either, which is great because that is typically when I'm getting ready to get off work and go home and.. do more work!