Compared to what makes up the GOP these days he was pretty great. That says more about what a dumpster fire the Republican party is than anything though.
Honestly, outside of saving Obamacare last year I can't think of anything he did as a politician I agreed with. Still though, if the Republican party was made up solely of McCains we'd be better off as a country. For that alone he'll be missed. Not as a politician who accomplished great things, but as an adversary you could respect, someone who at least in his own mind had the best interests of his country at heart.