I'm unsurprised by it.
I think Powell is an honorable man who was put in the horrible position of having to lie about Weapons of Mass Destruction to justify his President's war for Oil and Empire. I doubt he even knew he was lying: I think he's such a good soldier, he trusted that those above him were telling the truth. He got caught with egg on his face. It tarnished his reputation somewhat, when ironically, he was probably the last person in the Bush administration who deserved having his reputation tarnished.
He was a fall guy. He's gotta feel a little bit burned about that.
But, he's still a good soldier. You'll notice he's not expressing his opinion with great force. He said he won't actively campaign for Obama. He's being about as kind as he can be under the circumstances.
I wouldn't blame Powell if he blasted the Republican Party in general, and the Bush administration specifically, with every bit of verbal force he could muster. He's not doing that. He never was a noisy guy.
There was a time he himself probably could've been the first black President, but I guess that, "Yes, there are Weapons of Mass Destruction," routine wrecked any chance he ever had of doing that... not that he would've wanted it. He doesn't strike me as the power-hungry type.