Obito is a controversial character, at least kishi successfully deliver it.
Oh. Btw it all about executions.
And that's the key word, it is all up to the execution. I have voiced my positive opinion on Obito being Tobi, so I wont say about that now. Instead I will bring up why people have issue with Obito being Tobi, which comes down to the execution. Even though I LOVED ch. 599 in how they showed Obito's life before essentially "dying", I would be honest and admit that Obito's descend to villainy wasn't very well executed.
The idea itself is sound; a person, who was just like Naruto, becoming to villain due to death due to the circumstances of a childhood crush's death and the manipulation of a bigger villain. It would show interesting parallels between main villain and hero, and would show that, maybe, Naruto may have become a villain. We just need more reason other than Rin's death for him to ultimately, because that would make it seem as if Naruto can so easily become a villain if someone close to him die, and, on the surface, it sounds very petty. I know a majority of the villains became villains because death of someone close, it is just that a majority of those villains were already kind of messed up to begin with. Nagato wasn't always the most well-adjusted person around, there was always darkness in him. Orochimaro(?) ALWAYS acted like a creep, and Sasuke..........well, we all know Sasuke's deal. It was the same for most of the other villains, so was believable to think they would become villains or were villains. Obito was different though, because he was a good kid. He didn't seem evil, and didn't really seem to have any kind of darkness in him beforehand. He may have been lonely, just like Naruto when he was kid (PARALLELS!!!!), but also just like Naruto, he tried to prove everyone wrong by getting stronger. However, while in general he was nice kid, he wasn't perfect. He wasn't good fighter, and he felt very envious towards Kakashi for being better. That mad him three-dimension character, that mad him likable and believable.
Yet, supposedly, all that went away by the simple death of Rin? Sure, beforehand he was crushed by a boulder and fused with a Zetsu, but there wasn't any indication that was cracking up. He seemed the same like he did before he got crushed; he was still determined as hell to get back to his team and he rightfully laughed at Madara's ridiculous plan to change the world. Yet somehow,just witnessing Rin die, he's like
"Skrew it, and I am on Madara's side now, despite the fact that I mock his plan earlier."
And then suddenly he became the Tobi we all now love to hate, causing the death of possibly millions and manipulating several others to join him..............perfect sense 
Like I mention earlier, I do like Obito the character because he was, unlike most of the other current villains, he was very likable before his descend to villainy. An other thing that I mention earlier is the fact the idea, Obito becoming a villain, is alright. It just could have been done so much better than it turned out. One way would have been showing Madara actually getting through to Obito with his ideals, before Rin's death. That way he would be already debating with himself if Madara is right, and when he finally sees Rin die, then that would been the trigger that would convince him that Madara's right. Not only would show conflict in the character, but make his descend a lot more reasonable. An other idea that would work would have shown that after being crush he was also not mentally well afterwards. With a fragile mind, and little pushing by Madara, Rin's death could have been the perfect catalyst to push him over the edge. Or maybe, after Rin's death, he would work for Madara only under the pretense that he would do his bidding if would Rin. However, he would plan to betray Madara afterwards once he fulfills his promise, only to get corrupted by the action Madara makes him do.
I am only spit balling here, as there could have been MANY ways to make it better. Yet notice that I have always kept the part with Rin dying, that's because I see nothing wrong with her dying. While I feel kind of sexist to support an idea a female character dying to help a male character's development (WiR), but people DO do stupid things because of death. It is only human nature to allow death to overcome one's self, it is just that we need more for Obito. At least Nagato, they already imply that he wasn't all right up in his head before his friend's death, his death was just the wake-up call (that, and some manipulation by Obito, full-circle). We needed to see Obito already breaking before seeing Rin die, that ways it would seem reasonable and believable for him to join the dark side.
However, despite what I just said, I don't personally mind what we got in the manga anyways. Naruto never really had the sharpest of writing (though admittedly it came close around the second half of Part 1), so I wouldn't have expected them to get that complicated with a villain's reasoning. Besides, what we got I find really enjoyable. As mention earlier, 599 has been my favorite chapter in recent memory, and few of the scenes Obito's flashback were quite interesting to look at. Particularly the scenes where the Zetsus are cheering for Obito, and the scene where Obito attempts to hold Rin in his arms, only at first to realize that he can't touch her because of his justu (or whatever), is kind of heartbreaking. Not only that, yet Obito being the main antagonist brings emotional baggage to not only Kakashi, but, to some extant, Naruto (because he was father's student......and murderer). Not only that however, I personally feel sad that someone, who could have done great good to the world, did the exact the opposite of it. It creates an uneasy feeling in how if should understand his reasoning, or despise him the more. It has lead to some interesting scenes and dialogue, especially the part where he tells Kakashi that Rin's death wasn't the only thing that lead to his current situation (lier!) and how he mocks Naruto's naivety because he understands how he feels. The circumstances of Rin's death has also turn out to be more complicated originally thought, as most of didn't originally know what happen to her. When we first found out she died, we still didn't know about the situation she was in that allowed her to die, or how Kakashi was responsible. Then later, we found out Kakashi was the one that killed her, but we still didn't know why. We then find out that she jump in front of Kakashi so that he could kill her, because she had a tailed beast in her. With the circumstances of Rin's becoming more complicated than intentionally expected, I can't help but be invested in the storyline and desire to know more.
It really comes down to people's particular expectations of the manga, and how they interpretate the story. Having different interpretation is good, as it leads to good discussions, like the one we are having right now. In fact, because we are discussing this in such detail, then the story did something right for us to care.