yeah, agree with Feline, Mark Kendall played some outstanding stuff with Great White, which wasn't noticed because they were a "pop rock" band. same with Def Leppard, Steve Clark and, I think, Pete Willis ( if that names wrong, sorry ) were fabulous on their first three albums. and let's face it, Hysteria is the greatest "pop" rock album ever made!!
Adrian Legg was mentioned before, brilliant!
of course, the most highly rated underrated guitarist is George Harrison