I liked high school better. I interacted with pretty much everybody regularly (I don't really know what stereotype or clique I would be part of - well, class clown, but what else?), I felt popular (despite not doing any extracurricular activities - I regret not doing that), I felt like most of my teachers were like my friends. In college, it was different, the only real upside was not going every day. Many of the teachers felt more like bosses than buddies (though I feel some of them were to many of the other students), the interaction with classmates wasn't the same, there were many whom I wanted to interact with but when I talked to them they seemed to act like nothing was happening (well, nothing as a result of me) - and it's not like they wanted to focus on their schoolwork or were just quiet/shy (and I think some were), I regularly saw the ones who were ignoring me interact with other students regularly, in the same way that we all interacted in high school. There was one class in my second college semester that was the worst of it (and I had been in a class with about half of them my first semester and I either wasn't ignored that much or the lack of interaction hadn't hit me yet), but after that semester my interactions with other classmates got a little better (though I didn't finish college - who knows if I would have if either my interactions were better or if I cared more about my schoolwork and/or less on interacting with people?).
And maybe I would have had better interactions if more people I knew from high school went to my college and were in my classes. Some went to my college, a few were in my classes, but it was few. And I didn't leave town for college (I think a lot more people I knew from high school went to a different local college). I wouldn't say the classmates were more mature than before - I feel like many of my classmates (especially the ones who looked around my age) were about as mature/immature as the people I went to high school with.
Since I have graduated (18 years ago), I feel like I have seen most of the people I went to high school with at some point. Not exactly sure of the number of percentage, and I can think of some I haven't seen at all (or at least wasn't able to notice) since. And of course the high school reunion is a great place to see them (though I guess there were a lot more who didn't show up to my ten year reunion than those who did). In terms of not seeing most of your high school friends.... Well, I never really had many friends, at least when it comes to people I regularly hung out with outside of school or wherever I know them from. In fact I don't ever really hang out with any of the few friends I did hang out with anymore - and most of them still live near me.