I would say Mayer is a solid guitarist and a decent songwriter. I respect that. His music just does not appeal to me. I feel like he could do a lot more with that talent than some of this sappy, poppy blech he turns out.
That said, although I respect his guitar ability, I have seen him get absolutely schooled by some of his own generation's far superior guitarists. I once saw him share a stage with Derek Trucks and Trucks made Mayer look like a lost child. I can't imagine Mayer would even want to try to get on a stage with Jack White.