I've just started at a college 6th form.
You are treated more independently, but it's still like high school in the sense you have forms, homework, and rules of course. We still have rules like you're not meant to sit on the corridors etc.
We're allowed to wear what we want, which I really like. There's 2000 students, but obviously not everyone is in at the same time. There's a really good library, compared to the school ones which are really bad. There's also lots of seats, and quiet study areas.
I actually found that there's more extra-curriculars with college. I'm signing up to raise money for a school in India, and I'm also doing Law mock trials, and debating. There's also music clubs, drama clubs, things like chess, comics etc.
The downside is of course that you're not as close, as there's so many of you, that you'll only really know the people in your lessons, and extra-curriculars. But then again there is opportunity to move to a different class if you don't like yours. You also have a more grown up relation with your teachers, as you call them by their first name. People are more mature too, as there's no annoying Year 7s or 8s.