Yes McCain sided with the Dems in a number of fights in Bush's first term in particular. He was also effective at a lot of it, which many republicans particularly resented. But party loyalty is a poor reason to give for sitting at home or voting for Obama. If your own standard isn't party loyalty, pretending it should be for others is remarkably inconsistent.
Obviously, if party loyalty was my be all end all, I would vote for McCain. It isn’t and I won’t.