It's a "comedy" because it has a happy ending (relatively speaking), but it's not one by modern definition. It's a nice lesson in symbolism and is a pretty cool historical piece of work, if nothing else. It's cool to see just one person's ideas of heaven and hell though, and see it through their eyes and not in some kind of traditional narrative but one where the author writes himself in to experience everything. It's a very personal work, and a good one to make allusions to when you write stuff.