No uniform - you can dress up like you're going out of rock up in your PJs (unless you have labs, as mentioned above)
No daily lunchtimes with your friends - unless you make some with the exact same timetable
A bigger campus - you will probably get lost for a few days. And may have to travel for a loooot longer than you did to school.
Weird names for buildings/rooms - a lot different if you went to a small school
No one forcing you to do homework - apart from assignments, studying isn't actually compulsary for uni. Unless you intend to pass. And don't expect reminders about when your work is due; you'll only get told once.
No one forcing you to show up - some lectures/tutorials take a role call if you need a certain % attendance, but depending on the course you may never actually have to step a foot into uni (not recommended; even if you're half asleep in a lecture, you'll learn more than if you tell yourself you'll read the lecture notes but never do)
Completely different friends to the ones you had at school - you may only see them once a week, and they may live on the other side of the state from you. But you'll generally have a lot more in common with them as you've both chosen the same field to study.
More demanding work - I wouldn't go as far as saying it's HARDER than year 12, but you definitely are expected to learn more in a shorter period than you would at school. I swear some stuff covered in a one hour lecture would be taught over weeks at school
More stuff to do in your free time - Unis often have more food outlets/shops to visit and there's plenty of groups to join that'll give you a wider social circle and the occasional free lunch
All kinds of people - at school you only had people living in your area, your age. At uni there are people from all kinds of nationalities, all ages, and all socio-economic backgrounds. But everyone's really friendly
