this would be a hell of a time paradox than..
maybe Obito would have summoned some god like strength and avenged Kakashi's death. but he would be burdened for letting him die. the girl that he loved, Rin, would be devastated and he would blame himself for it.
he would vow to himself to never let a friend die and his new found determination would drive him to go from a poor excuse of an Uchiha to one of the best Uchiha in history. also Rin would have never died because Obito would have saved her. so Rin would actually be in the story.
Obito is a few years older than Itachi, his reputation for being a hero in war and helping destroy the bridge would have been known.
he would have been Itachi's and Shisui's sensi. Itachi wouldnt have killed Shisui because Obito taught him that to abanonned friends make you scum and blah blah.
but the Uchihas wouldnt have staged a coup de etat because Obito would have spoke agaisnt it. and being well respected and one of the strongest Uchihas they would have listened to him.
Itachi wouldnt have to murder his clan, the Uchihas would still be around and Sasuke wouldnt be emo. Sasuke would have grown up happy and befriended Naruto. Naruto wouldnt have been such a clown and lonely to begin with and taken after his friend Sasuke and been a genious.
Obito would have been in charge of team 7. Sakura would have been so useless because she has to compete with 2 geniouises, Sasuke and Naruto. Naruto would have mastered Kyuubi by the chunnin exams and have Kyuubi Chakra Mode automatically making him Hokage right from the start. Jiraiya wouldnt have died because Naruto would have never let Jiraiya go on that mission. Tsunade would have eventually came back to train Sakura.
btw Obito would have found Madara and kill him himself etc etc
yeah thats what i think.