Just managed to run through this entire thread... Wow. A lot of varying opinions.

One thing that struck me as very odd was someone claiming Paul McCartney was an overrated guitarist. Why did his name even come up? He mostly plays bass, piano, and is known for his songwriting. I don't believe I've ever seen anyone claim that he's a guitar virtuoso. He may have played acoustic guitar on some of his solo stuff, but I don't remember ever seeing a six-string in his hands as a Beatle. His bandmate George Harrison on the other hand was definitely underrated as a guitarist.

As for overrated vs underrated, I'm not a huge fan of shredding, so not much of the Satch/Vai/etc stuff appeal to me. Overrated? I'll leave that to others.

Hard to say too many guitarists are underrated, but one that strikes me as flying under the radar of a lot is Joe Walsh (solo, James Gang, Eagles). His solo stuff and his band work, his lead and his slide work, the guy makes anything he's playing sing - Tele, Strat, LP, Gretsch, or his more recent guitar, a custom Carvin - doesn't waste notes. To me, most of all, he does this and appears to be having fun doing it and doesn't take things too seriously (listen to Life's Been Good - you might be able to find the film clip somewhere). Saw him on two Eagles tours of Australia and really regret not being able to go the last time they were out here in 2015.

While I won't say he's underrated, John Fogerty (Credence Clearwater Revival) surprised me when I saw him live a number of years ago. Strapped into a Music Man of some sort and shredded like Vai. His CCR and solo stuff though was good at fitting the song.