The flexibility to approach my project in the way that suited my own skill set, the support from my co-workers in pursuing my ideas, and being in a open-space work environment collaborating with other passionate people. I never felt like "just an intern". I was a part of the team, through and through.
What I wish was different
I wish I had a larger network of interns to work with. It was a small office, which had its benefits because the relationships I developed with the program staff was incomparable. But I wish there were more interns supporting their work, and a community of entry-level students to support each other.
Speak up. There are no bad questions -- but there might be real consequences if you don't allow yourself to ask for help. It's a necessary challenge and a muscle to exercise.