For the majority of those who are upset about this, it is not because it was so obvious.
In the span of one year, Obito went from being a knuckle-headed, got his @ss handed to him by Gai twice, got his body crushed by a mountain, bottom-shelf shinobi, to being a top-notched, able to mind fuck Yagura (a kage who had apparently mastered his bijuu) and control an entire damn village, as well as go toe to toe with his mentor, who was the only shinobi known throughout the manga to have a flee on order sight, not to mention that he annihilated the ANBU forces that were guarding Kushina during Naruto's birth.
And oh yeah, there is the slight issued of Minato being Hokage before Kishi stated he actually was Hokage. Not to mention that it was stated by Tobi that he was the one who gave Nagato his rinnegan, and yet Nagato is actually older than Obito. That means that apparently before Obito was supposedly killed, he already had awakened the MS, f'n warped to Amegakure, and given the damn RN to Nagato while he was still a knuckle-headed twerp.