Why would it be a let down for some if it is Obito? If I recall, Obito had a very profound effect on Kakashi and Kakashi is the way he is today because of that. And to some effect, those values and beliefs were passed on to Naruto and the team. The past makes the future imo. Some could go so far as to say that Obito was in fact the Naruto of his day while on Team Minato, hell they even had some of the same styles. They had almost the same personality too. They also had the exact same feelings of their village, to protect it even at the cost of their lives. I think that Sasuke is a great rival to that of Narutos own power and beliefs...
butwho would be an even greater rival for Naruto than Naruto himself? Though it is a very messed up way of reaching his goal. In a way, if it truly is Obito then that's someone from Kakashi's and Gai's past yet again they truly loved and it would be hard for them to try to stop him as Naruto has problems stopping Sasuke.
IMO that makes for some great storytelling in a series and I welcomeit.