Jury's still out at this point[1], but this certainly makes me optimistic. Or, at the very least, intensely interested in what this new arrangement will yield.
[1] He seems to certainly not be a bad CEO if we're talking about the set {All CEOs}. But you'd have to be really really good to not look awful if you're following Jobs.
I don't know if anyone ever doubted Tim Cook as a good/credible CEO. The only issue is whether or not he can be jobs-level which is unlikely but remains to be seen.
[1] He seems to certainly not be a bad CEO if we're talking about the set {All CEOs}. But you'd have to be really really good to not look awful if you're following Jobs.