I have just installed KDE 4.9 in Linux Mint 14 the easy way. Just type sudo apt-get install kde-full to install all of the packages in one go. Since I have my dual desktop configuration laid out in my /etc/X11/xorg.conf file I had a properly working dual screen desktop as soon as KDE started up for the first time. In the accompanying screenshot you can see what the vanilla KDE desktop looks like with the default theme and the KDE wallpaper. In Ubuntu you type sudo apt-get install kubuntu-desktop to install KDE but at least Linux Mint has an equivalent command that can install the whole KDE desktop for you in one go. The KDE 4.9 desktop on Mint 14 is very fast and usable; with nothing to complain about in terms of performance. In the screenshot to the right you can see the settings I am using for my task manager; these settings ensure that task manager buttons will appear only on the screen that the application is running on. KDE is a very configurable and themeable desktop interface; there are a good selection of KDE themes that are very good looking.
This posting of mine has a good selection of KDE themes: http://www.securitronlinux.com/linux-mint-2/windows-7-lookalike-kde-themes-how-to-make-linux-look-like-vista-or-windows-7/.
How to make KDE 4.9 look like the old KDE 3.4 interface with the Crystal theme: http://www.securitronlinux.com/bejiitaswrath/useful-kde-4-8-0-tips-how-to-make-kde-4-8-look-like-kde-3-4/.
How to install themes and wallpapers in the KDE desktop the easy way: http://www.securitronlinux.com/bejiitaswrath/installing-themes-and-wallpapers-in-the-kde-4-7-4-desktop/.
There are many more themes and wallpapers available for the KDE desktop. Look here: http://kde-look.org/.