If you are used to looking at the Masks Panel, the Adjustment controls for Adjustment layers and the 3D options, they have all been consolidated into a Properties panel. This helps reduce clutter.
When you go into the filters menu, you might think a lot of filters are gone. Actually it’s just the clutter that’s gone, all the missing filters are tucked away under the Filter Gallery.
Definitely worth mentioning is Preferences can now be imported and exported. This is great for people with lots of custom brushes, shapes, actions etc. I know, I have several computers and it’s difficult to move them all over manually, and I always lose a few when I upgrade to a new version of Photoshop. Photoshop CS6 offers the option to migrate old presets over on launch; I have to say that I love it!