"Good" and "Bad" are subject to individual taste, but "Underrated" (or "Neglected") and "Overrated" are a little more objective (or to be more accurate, these terms are "more intersubjective" as opposed to "intrasubjective") because they're judgments about value judgments made by groups of people.

The passage of time can winnow out some overrated bands and bring to light people who were ignored in their own era.

According to my taste / listening history, Yes, Genesis, Jethro Tull, The Police, U2, Emerson Lake and Palmer, Eric Clapton (as a solo artist), and lots more popular progish / classic rock era musicians are overrated. The jury's still out on The Smiths, The Clash, and Rush because I haven't heard enough of their music or for a long enough time. I think King Crimson and Pink Floyd deserve their fame, but fans of those groups tend to ignore similarly talented bands, so in a relative way, they're a bit overrated.

Overall, an intelligent appraisal of popular musicians and the phenomenon of popularity.