I think McCartney at his best is untouchable. But no one is perfect, and if I had to criticise him for something it is that you hear nothing of the man in his songs. That doesn't mean he doesn't make great, amazing music.
But i do get the feeling that he can write great songs in his sleep ( reckons he did with Yesterday.) I just wish that sometimes he would bare his soul a little. Not saying he has to do it all the time, or that all great music has to have some inner emotion. ( but maybe it does)
McCartney can be a little Stock-Aitken-Waterman sometimes. Great tunes, but strangely heartless. As I've said before I wouldn't put Paul on at 2 am. But I would on a nice sunny day.
And I agree, The Beatles are at their best when John and Paul's styles are contrasted, like Paul's pure pop of Penny Lane and Hello Goodbye against John's haunting Strawberry Fields and I Am The Walrus. Rock and roll genius.