A lot more being accountable for yourself than high school. Professors are there to teach and most will help if you ask them for assistance but unlike high school they won't go out of their way to keep the people afloat that don't want to put in the work. They figure if you're there you better have an idea or two how to do that yourself as well as work to do it.
Less emphasis on how you look going to class too. A lot of sweatpants and pajamas after the first couple of weeks.