I found the ending depressing (and too simple), too. I got the impression, though, that I wasn't expected to be depressed by it-- After all, the social order remained intact, family lines continued, and all of the characters ended up where they were supposed to be. I think the author expected us actually to believe that the twins had suddenly become entirely different people through divine intervention and to want them to become different people.

But for a deus ex machina to work, the audience has to believe in the god in question and accept that it has the power to fix things. To be honest, given the culture in which the story was written, I don't think there was a way that there could be a happy ending that modern readers in the United States would find believable and satisfying.