One of the big visual changes just happened in KDE 4, the transition of kdelibs to the Oxygen Icon set. This transition is still in progress, and it includes a massive icon naming scheme change that affects thousands of files. But, the Oxygen artwork project much is more than just an icon set, it’s a unified way to do artwork for KDE 4.
So far KDE 4 is coming along nicely, but still has a long way to go. Oxygen seems impressive as well, especially regarding independent resolutions for enabled applications/games. KDE 4 looks to be changing the naming schemes of a -lot- though, so upgrading from 3 looks to be a fun task.
Source: KDE.News