You can count me in with those who think that Unity is a mess. I much favor Mint main edition over any other distro, and Gnome 2 over any other desktop environment. That said, with Gnome basically abandoning Gnome 2 (no the "classic" desktop in Gnome 3 is not close to being the same thing), and ubuntu moving to unity, I currently find myself in a bit of a lurch.
For me, If unity continues the way it is going, I will not be adopting it. A ton of suggestions have been made. Lets see how many are accepted and worked in. Personally I would suggest that they allow the Launcher (ie, the dock) to be unstuck from the left hand side and placed wherever the user wants it. also when opening the main menu, it would be nice to see categories or all my apps. instead what you see is a limited selection of apps and a bunch of suggestions of stuff to install? who thought that up? I don't want to be advertised apps by basic operating system functions. In a very un-linux way, unity is not terribly customizable, and I really hate that. On the plus side, I love the floating scrollbars and think that they out-did even apple with the global menus (brilliant!).
Don't get me started on Gnome 3. Boy what a mess that is. Sure, it is much pretier than Unity, but it too is unecessarily rigid and overly complex, for no apparent reason (other than to provide eye candy that is). I do like their approach to the apps drawer (a format Ubuntu should consider adopting) As well as the integrated search and notification features. whoever came up with the idea of getting rid of max and min buttons should be taken out back and drop kicked. Don't get me wrong, activating the feature by dragging and dropping windows to the edge is fine, but if you aren't going to use the space for buttons, than why is there a giant chunk of unused frame at the top of every window?
Meh.
IMHO Mint does the UI better than anyone, especially once you apply a few personal mods.
That said, come this fall, when Ubuntu drops gnome2 entirely, mint will need to have a valid replacement. at this point, I don't think Xfce is it, but f worse comes to worse I might be adopting it. Maybe the will have worked the bugs out of LMDX by then.