Powell supported and voted for Obama. That is all anyone needs to know.
The why is more important than the what. Foreign Policy.
McCain campaigned on a NeoCon policy and Obama campaigned on Realist foreign policy.
Initially, Powell merely supported Obama's foreign policy positions, which he was condemned for, and after which he would announce that he would vote for Obama.
Powell wasn't the only republican realist praising Obama and criticizing McCain. Kissinger, George Schultz, Scowcroft, and others also.
This issue is still playing out today. A few months ago Jeb Bush met first with prominent NeoCon Paul Wolfowitz and then with prominent Realist James Baker. Bush wants to signal that both NeoCons and Realists would have a role in his foreign policy.