I wouldn't necessarily want to be back in undergrad at my age, but college was like a ******* fantasy camp. I can't imagine being in college and not enjoying it. Grad school blows, but I'm looking forward to the real world.
IMHO, the best part about college is not owing any kind of responsibility to other people, only yourself. No wife, long-term girlfriend, children, etc. You can do what you want, when you wnat it. It was that unlimited freedom in your personal that made college great. I have not doubt that each stage of life can be great, but always in different ways.