The fact you can "install" it is simplistic. Manually adding a desktop environment on top of Unity is not the same as one carefully groomed to work seamlessly, which is what Mint delivers.
Dislike Kubuntu/KDE (I've used Ubuntu/gnome2 for long enough that I can no longer bear the look and feel of KDE).
Maybe I should try Lubuntu... I've lost faith in the Ubuntu project though, I don't think they're capable of making the right decisions.
I mean they put the package in the repo! The whole WM/DE thing is a derail, that stuff is just claptrap, window dressing, extremely easy to replace and we have a huge selection of choices.