Check out this analysis by Jay Ambrose in The Washington Times of John McCain as a candidate for President. I think he gets the pluses and minuses of the McCain character just about right.
No question, McCain has the right goods on national defense and the war with islamofascism. He has better credentials on these key topics than any other candidate of either party. McCain understood that Rumsfeld was wrong about Iraq and said so, when nobody else in public life had done so.
Unlike Ambrose, I am not especially infuriated by the McCain-Feingold campaign finance limitations. That issue is pretty much inside baseball; that is, of interest primarily to special interest groups with deep pockets who want to buy influence and the politicians who need their money and will sell their votes.
On the other hand, Ambrose is correct that McCain's advocacy of amnesty-with-a-fig-leaf for illegal immigrants shows McCain has a tin ear when it comes to understanding the views of his party's base voters. If stopping illegal immigration isn't issue number one with Republican voters, it is surely in the top two or three.
There comes a point at which being a maverick gets to be a real pain in the neck to everyone else. McCain passed that point and never looked back. I suspect he decided, decades ago in that North Vietnamese prison, that he would do what seemed right to him and the heck with the opinions of others. As long as he represents only himself, that is fine. When he proposes to represent me, then I want him to be interested in my opinions and to attempt to further my interests, not merely his own. He still needs to convince me that he wants to represent mainstream Republicans, to move our agenda.