First of all, nothing this oppressively sad could ever be anything but a tragedy. If you yuck'ed it up during 90% of this movie, you're probably a malfunctioning robot.
Not only that, but Citizen Kane has all the elements of a classic tragedy. Let's see now… a character who seems quite admirable at first? Check. A really strong dose of pride that gets out of control over time? Check. A final death where the hero recognizes his mistakes… only to realize it's too late? Check and check.
Oh yeah, and let's not forget the trail of discarded friends he leaves wherever he goes. There's no doubting that given the right circumstances, Charles Kane might have been a truly great man. But that's just not how things work out because his ego/hubris keeps him from learning from his mistakes.
Yup. Our man Kane would feel right at home at a (depressing) dinner party with Hamlet, Othello, and Macbeth.