on win8 classic shell doesn't even replace the file copy dialog (yet at least)
as for using the start menus search, at least in the newest versions it does initiate a windows search behind the scenes, and just display the results. (it definitely uses the windows search index)
as far as a start menu, it can be set to reproduce either cascading start menu (the sub-menus come out of the side of their parents), or the inline/windows 7 style
the only modifications it makes to explore windows (when you open my computer) is adding a toolbar, that can have customized buttons) (windows 8 already allows for an up arrow)
any other questions might need to be more specific, or you can just try the program out yourself