While (almost) everyone was complaining about the new GUI in Revit 2010 in the beginning, acceptance seems to have set in.

If, however, you still don't like it and want you old 2009 GUI back, read this article from Autodesk. There you can donwload a workaround to get the 2009 GUI back for your new Revit.

But be careful, there will be no support for this or any other guarantee, that it will even work. So, try at your own risk!