I listen to this cat and sometimes he really lets his chops fly. A really good talent. then I'll listen to some other stuff and it's elevator music..total mindless trash.
Posers like Kenny G and Dave Koz live of of the shoulders of the jazz greats, but I give them a pass because they've never really professed to be jazz masters. But Metheny has proved that he can lay it down. Given that I hereby charge Metheny with being the jazz artist who has most neglected his talent. An honest to goodness sell out way to often.
He's been around making magic for over 30 years. Everyone has their ups and downs professionally and personally. so it's only natural that his history sort of looks like your green rating graph. You will have to agree that when he's good, he's good. (OK, we're related) But the above, still true.