He gave in to the RNC advisors and others around him that time around. Palin obviously turned out to be awful (maybe not strong enough a word) and he didn't care for her very much either, but I imagine he just wanted to get into office so that he could institute what he felt were good policies.
I think he was fundamentally a good person and would have been a good leader, though of course we can debate the merits of his policies. Everything being equal, I'll vote for the person I believe has the interests of the populace at heart.