Someone once wrote in a forum that one of Paul's greatest strengths is also one of his fatal weaknesses. They were writing about his eclectic musical output, and I agree.
Most bands have a "sound" which may or may not evolve over time. Sometimes a band will experiment with different "styles" or genres, and apply them to their songs, but in a way that leaves the foundation of their "sound" intact.
But not Paul.
Every 70's and 80's album seemed to be a complete musical departure from the one before it. I think during the Beatles, this tendency was tempered by the other Beatles and George Martin, but left to his own, Paul was often extreme. The problem with this is, it alienates casual fans. Paul picked up a bunch of new fans with 'Back To the Egg', that eagerly waited for the next album, only to be dumbfounded by 'McCartney II'. Likewise, fans of Paul's softer 'Band On The Run' or 'Red Rose Speedway' rock sound were confused by 'Back to the Egg'.
'McCartney II' is an OK listen, but it should never have been a mainstream release. What he should have done instead was a LIVE album of new songs with a consistent sound like the 'Coming Up' single. This is what the public wanted, (supported by the fact 'Coming Up' topped the charts). A few songs from 'McCartney II' could have made it to such a live project with some reworking, maybe a few unreleased songs...
How awesome would that have been?