What I liked
I loved learning what research is actually like in the "real" world outside of school. I also loved having the independence and time to try to figure out problems on my own. So many of the concepts I was working with were new to me, and so I had the opportunity to gain skills in finding answers for myself.
In addition, the REU program and the other people that I worked with were great! They were all very supportive, and always willing to help me when I needed it.