He was not a naturally-talented guitarist. If you read Geoff Emerick's book about the Beatles Here, There and Everywhere (he was the chief engineer on Revolver, Sgt. Pepper ..., and Magical Mystery Tour), George often had a difficult time working out and perfecting many of his guitar solos. Geoff remembers several occasions in the studio when George would keep the others waiting for ages whilst he struggled with a particular solo. Paul sometimes played the lead instead, often nailing it on the first take.
BTW, I don't think anyone mentioned Jeff Beck - an amazingly versatile guitarist - I love his jazzy stuff.