I can't speak for goalkeepers in the past since I don't like to comment on players I never watched before, but Neuer is without a doubt the best keeper I've watched in my lifetime.
As a sweeper he is second to none, and so many keepers in our generation try to play the sweeper keeper role and none of them do it as good as Neuer. In the box, his actual goalkeeping is top notch. His shot stopping is superb, his physical presence and command of his box, coming out for crosses etc are all great. His passing is quite good as well.
It's difficult to imagine how a keeper could be better than him really. He just has so much to his game. Even if there may be some others that were marginally better at shot stopping or something like that, his ability as a sweeper elevates him above them all for me.