Ok, if you have not already come this far, don't read the following as these are major spoilers:
Orochimaru actually brought back the 4 former Hokages.....
Aside from the cheap factor (which I personally don't mind) this is a huge event.
This will mean Madara is going to shit 7 colors of chakra when he once again sees his rival....Hashirama.
Minato will see his students, he will see that Obito became a douche and Kakashi a good guy.
Sarutobi will learn...of Asuma's death...
Tobirama...well I don't know about him. :P