Overall...I agree with the end result - especially the new features that are not icon or location dependent such as hot corners, tabs, etc. I just think they could have done a few things to make the transition an easier one. For example, you can revert back to the originally layout but you cannot revert back to the original icons. People speak of muscle memory but that is easily solved with the old layouts and ONLY for those commands that are in that old layout. What I would have preferred is the ability to switch back to the old icons just to re-orient yourself to the layout first and then (when you are ready) re-orient yourself to the new icons. Even when muscle memory kicks in, if the icon is completely different you have to pause for a minute, hover over the icon a bit, see the name come up and then once you have confirmed this is the command you want, you proceed. That actually slows you down more than you may think.
The fastest way (IMHO) to learn the new UI is to create your own layout. Redo everything and rebuild it how you want it to work. The pedantic action of finding and placing each icon where you want it both teaches you where it will be located and what it looks like. People are saying that it takes about a week of use to become familiar with it but I think re-building your custom layout will get you there much faster (hours not days).