I don't think Livingstone is an idiot - he's at least tried to put together some kind of transport plan for London, which is more than Boris will do. And he wasn't popular with Blair and Brown for his very public dislike of the PPP schemes which he was forced to use - one of which wasted at least £3bn of public money for very little result.
But he has drited towards authoritarianism, which isn't going to win him any votes.
Like Nu Labour, if he loses it's going to be because of popularity, not because of his actual record - which isn't an unmitigated success, but is probably as good as anyone can expect from the current crop of UK politicians.
I have nostalgic reasons for liking him. When he was head of the GLC during Thatcher's hell-in-a-handbasket years, he tried to cut the cost of using tubes and busses down to positively European levels - at least until Thatcher abolished the GLC from under him.
So I think his intentions are good, but he does have an egomaniac side which doesn't make him very likeable, and often leaves him less effective than he could be.