I didn't vote for McCain for the same reason I wouldn't vote for any member of the GOP--he'd gone way too far in embracing the socially and economically conservative party line. Until they change their platform to something more reasonable (by my standards) in terms of social equality, economics, environmentalism, and the role of science in informing policy, I don't trust them. I liked Obama better politically as well as personally.
McCain is more palatable than many Republicans and has been more willing to reach across the aisle in the past (as with McCain-Feingold), but once he decided to seek out the approval of his party as a presidential candidate, whatever his personal beliefs may have been about everything from abortion to the environment went out the window. As for his choice of Sarah Palin as running mate, he chose someone who exemplified the worst form of simple-minded conservative populism at that time. I don't know if that's what he wanted, or if he really thought he was reaching out to moderate and conservative women with a running mate who was (at that time) unknown and not controversial, but he didn't vet his choice well enough. She was a complete joke.
Maybe he feels like he's able to be his most authentic self again, now that he's in the home stretch of his political career and very likely not long for this world. I know it can't be easy being a moderate conservative these days, but I don't feel that sorry for the few who remain. They bedded down with the devil of extremism, and the more you give in to the far right, the more the far right demands. Overall, I haven't seen a lot of spine on the right when it comes to uniting against a man many of them allegedly are worried about in private.
Hindsight being 20-20, though, it was only a matter of time until one of the GOP's populist "jokes" ended up in the highest office in the land.