I started running while living in Nashville, TN, a pretty hilly city. Because I learned how to run them well, I’ve always been okay with hills. I kind of like the visual goal — get to the top and then get back down. A flat, straight course is great for a fast time, but can be pretty boring if there aren’t enough curves to keep it mentally interesting.
Check out this excellent video on hills (only 3 min long) from a 6-time Ironman athlete.