Gnome and KDE went through similar histories. The maintainers (for some unkown reason) decided they had to radically change their product - just as Ubuntu decided to introduce a totally new gui a few years ago. The verdict with Gnome is almost universal - the new Gnome (Gnome 3, which you have with Centos 6, unfortunately) stinks and isn't getting any better. Nevertheless, those who offer Gnome - e.g., Redhat, SUSE, others - offer only the latest version. Redhat has made it the default. Their motto is "just get used to it". But there is one hugely positive development: Mint decided to fork the old Gnome, Gnome 2. Mint offers 2 versions of Gnome 2: the Cinamon gui and the Mate gui (pronounced matey, a type of tea). I have no experience with Cinamon but love Mate. I am using it on my main computer. I noticed recently that Fedora also offers a Mate variant. My guess is that eventually most of the distros will; they will offer their main gui, whatever it is, plus Mate, XFCE, LXDE, etc. I am guessing that Gnome 3 will eventually go away.
KDE4 is like Gnome 3 but actually improved as it developed. One of its peculiarities is that it offers 5 (I think) different ways of laying out and using the desktop. One of them - called Folder View - makes it quite similar to the discontinued KDE3. I have instances of folder view KDE4 in my PCLinuxOS and Mepis setups, and like it. Be aware, however, that KDE3, like Gnome 2, has been forked. If you go to the Trinity Linux website you will find that there are people who have rejiggered Debian, Ubuntu, and PCLOS with the KDE3 gui. In fact, one of my partitions is running Debian Wheezy with KDE3. One of the best things about KDE4 is the Dolphin file manager which I have imported into all of my non-KDE setups. It is far, far superior to every other file manager, including the old Konqueror, which Trinity KDE3 still has.