Kenny G appeals to a certain market. Pat Metheny to a very different group of people. Kenny G's very good at what he does and goes out to entertain. PM tends to be more self-indulgent when he plays.
I'm not a fan of either of them, although there's something about Kenny G's tone on sop that really impresses me (just destroyed all my credibility now).
Sadly there's a tendancy to trash someone's music because it doesn't appeal to you. And in the jazz/sax arena Kenny G is public enemy No. 1. But I don't think it's right. Kenny G's music may not be what you want to do or listen to, but it doesn't destroy it's validity for others. Because you don't like someone's music, doesn't necessarily mean that it's poor or bad. One could equally say the same about Michael Nyman, or Perry Como, or Tom Jones.
Each to his own.