Solos on "Pulling Mussels from a Shell", "Black Coffee in Bed", and (especially) "Another Nail In My Heart" are everything guitar solos are supposed to be -- well thought-out, well played, pretty much perfect.
Lost in the shuffle because Steely Dan used so many brilliant guitarists at different times, but Walter Becker was a pretty darn good player when his number got called.
Isaiah Mitchell is such a talent. I don't know if he is under rated as much as maybe just not well known. Isaiah is rated highly from everyone I know that is aware of him.
Isn't it like as soon as you say "underrated," but then mention them, they automatically leave the ranks of the underrated? I think Jimi Hendrix is super underrated.
Peter Tork - He could play multiple stringed and keyed instruments including: guitar, bass, harpischord, banjo, organ, and piano. Stephen Stills was quite impressed with Pete's talents!
I reckon Nash Kato & King Roeser of Urge Overkill (never knew played on what) were always interesting, esp on 'Jesus Urge Superstar' (despite it's ****ty sound.)
I have seen Jerry a couple of times live with Eilen Jewel, once my head was pretty near his cabinet, wonderful player, also hes about 80 but lost none of his chops.
He is not really "underrated" but Peter Buck is one of the greatest rock players who seldom gets mentioned in the "look how fast my fingers move" world.