Obito realized, or at least thought to have realized, that hope does not exist. Despite, Naruto - who reminds Obito of his younger self - keeps on clinging to hope and doesn't give up his ideals. That's the reason why he so desperately wants Naruto to experience the same pain he did, to prove Naruto, and himself, that only his way is the right one, and that sooner or later everyone will become like him. But the more Naruto resists, the more he dissociates from Obito's ideas of peace and reality, the angrier he becomes, because he seems to realize that there's indeed another way; that there's more than just despair, hopelessness and loneliness. And the more that happens, the more desperate he tries to crush Naruto's hope.
Obito (or rather Tobi) used to be my favourite character, and I used to dislike his sudden change in character after his mask dropped. But I'm getting used to it. During his fight with Naruto and Kakashi, he got more and more emotionally involved; his anger towards Kakashi came more and more to the surface, and he began to see parallels between himself and Naruto. With that being the case, it's no longer true that he doesn't care about 'this' reality. He's losing his cool, and that might indeed lead to his downfall.
After all, Obito's character isn't so badly written; the only thing that I dislike about it is that he does everything only because of Rin. That's not a bad thing, but Kishimoto didn't put even the slightest emphasis on the actual relationship between the two, or went beyond the surface. If there was a truly deep, emotional, invaluable bond between the two of them it'd be all fine, but Rin was portrayed as nothing but a crush of Obito; that's what really bothers my.
