Presumptuous horseshit aside, there is a difference between being a high school student and being a working adult (I will refrain from "the real world," as either side of the coin is someone's reality regardless). For me, the biggest changes out of high school and college were mainly the act of having to actually support myself - paying my own bills, going to work every day, 401K, health insurance, doing my own grocery shopping, etc. It's stuff I'd never really had to deal with before. Oddly enough, I enjoy the independence, even if it could get stressful.
Probably the other huge change was how much bigger the world suddenly got (I spent a couple of years working between college and grad school). High school is a small pond, comparatively speaking. I didn't notice that while I was there, but my world in high school was very small...and probably a lot more structured - you know where you have to be each hour of the day while you're at school. When I was out of school and working, everything just seemed so much "bigger" to me - I wasn't confined in a building full of kids around my age; I was now in a much larger tank with a much larger variety of people to talk to and deal with regularly. It can make you feel very small, but the fact of the matter is, in a world of nearly 7 billion people, you ARE small!
However, people seem to get hung up on the idea that their "smallness" is a bad thing...I don't think it is, really.
Interests-wise? Hrm...I suppose my interests have changed a bit to things that I can apply to my work or to some practical use. At the same time, I've seen my focus in my personal life change from mostly myself to mostly other people. I don't mean that I'm constantly comparing myself to other people (that isn't simply a high school thing - people my age and older do it too...it's an insecurity/maturity thing), but I suppose I should say that I pay closer attention to what they're saying, what they're not saying, how their actions reflect who they are, etc. I didn't do that much in high school - cognitive development-wise, those skills haven't quite solidified yet in adolescence.
High school is a stepping stone, and an important one, and it prepares you for the next stepping stone. And so on. Life changes dramatically after high school is over, but don't worry - it's usually for the better. :)