Usually it has more to do with the professor than the topic.
"Dinosaurs" was obviously great.
"The Supreme Court" was great because the professor was really smart and gave great history lessons, and I completely disagree with his politics but I loved the rationality of his thoughts. Learned a lot about US history and how the government worked, really interesting class.
"Game Theory" was fun. It was a senior-level econ class with lots of math, and I had never taken an econ course and didn't know anything about econ, but I was a math/physics major so it wasn't a big deal. I didn't always know what the axes were on the graphs (what is a Supply and Demand curve?), but my girlfriend sat next to me and told me the axes so it was a fun and easy A.
I took a middle-eastern studies class that was great because it was 60% female and the girls were gorgeous. I spent all day in classes that were 90% male, so this was quite a welcome turn of events.
Worst experience was an Africana Studies class. It was awkward to be a white guy. The TA wrote some offensive comments on the first couple of papers that she handed back to me, but I showed them to the professor and she got thrown out. I actually learned a lot in the class, and the other students went out of their way to be warm and welcoming.