After installing Fedora 11 in a virtual machine, I opted for KDE 4 to see how it looks. It was quite interesting and pleasing visually. I was impressed and it made me use the Linux desktop for a long time in one session. Obviously, there was a lot of work and thought put into the design and implementation of KDE 4.
KDE 4 is what a Linux desktop should look like if Linux should become a mainstream desktop operating system. I do not mean to ignore Gnome. However, I enjoy using KDE 4 more than Gnome. Check out KDE 4 and see if it suits you.