I may be the resident Sasuke fangirl around here, but even I can't defend much of what he's been up to lately. While I will hold to the hope he gets redeemed in some way, shape or form before the end of the series, at this point he's basically a villain. I don't think all hope is lost for him, but he neeRAB Naruto to knock some sense into him before he completely goes down a path he can't return from (meaning soon).
He was a good rival in part 1. He opposed Naruto and they pushed each other to get stronger. They had opposing viewpoints but both had distinct impressions on each other. However, the minute Sasuke left Naruto lying in the Valley of the End, he was no longer a rival. Since the two went close to three years without seeing each other, they didn't really push each other to improve (well, Naruto wanted to be stronger to get Sasuke back, but eh...) and whatnot. To be rivals, you need to be in competition with one another in some fashion, and the two are on quite different paths at this point so the definition doesn't fit.
However, I think he makes a good goal for Naruto. The series is all about the new generation surpassing the old and the most important dynamics in that regard are Naruto/Jiraiya, Sakura/Tsunade and Sasuke/Orochimaru. Jiraiya was unable to save Orochimaru, so for Naruto to completely surpass his mentor, he has to save Sasuke--which is why I still hold onto hope for Sasuke when it seems like no one else does