I think Madara was a big influence in Tobi's life, or they are intertwined somehow. I'm a little more pleased there's a deeper story behind all of this, rather than just having Madara summoned only to disappear without any plot or reasoning behind him coming back.
Now we get to delve deeper into the past, with many questions like, "How does Madara know so much about Edo Tensei?" I mean he seemed to know what was going on immediately the moment he was brought back, which let us know he had some knowledge about it.
We also have to ask ourselves, "Did Tobirama reveal the secrets of edo tensei to Madara in his life time?" while at the same time making Tobirama's death/disappearance a little more interesting.
Whatever happened in the past between Senju and Uchiha is still very much a mystery, and there's so many unanswered questions, which is keeping me hooked!
