The KDE Plasma desktop has surged to the top of the class with regards to the various Linux desktop offerings. It enables you to have the best of both worlds re using the Gnome 3 kernel with Ubuntu ot Linux Mint without shackling you to the much unliked Unity, the underdeveloped Gnome desktop or the below scratch simulator that is MATE. In addition it has so many lovely features that none of the mentioned desktops have and you have native composting as well as the ability to utilise Compiz. The down side though is that when you install only the plasma-desktop, your GTK applications look really primitive.
One way to rectify this is to install LXAppearance. You can find it in your Synaptic package manager. It is a new feature-rich GTK+ theme switcher able to change GTK+ themes, icon themes, and fonts used by applications. ONce installed you can find it in Start>Applications>Settings as "Customise Look and Feel". You can do all your GTK customisation there. One thing to note - when customising change your mouse pointer there to macth your Plasma mouse pointer ( if you have changed it on the Plasma desktop), or it the mouse pointer will change every time you mouse over a GTK application to the default GTK mouse pointer.