Oh dear. It's one of those threads that mention multi-million selling artists and call them underrated. Do you know how much commericial and critical success Alice Cooper and Thin Lizzy have had?
Underrated, to me, would be someone like Tim Buckley or Nick Drake. But, despite being ignored during their brief lifetimes, these beautiful souls are now fairly well known. Nick Drake's fame started in the 1980s (he died in 1974, I think) and has only grown since. But these are still more underrated than most of the acts mentioned here are.
When I mean underrated, I reiterate, the fact that they are extremely overlooked nowadays. Sure they have their fanbase, but they are widely ignored by this generation.
When Alice Coopers 'Along Came a Spider' album came out last year, there wasn't much hype, but the usual fans knew the songs were brilliant.
Although I usually like older, "classic" rock bands (mainly 70s/80s), I think that Alexisonfire are really underrated. They're not to my usual taste, but they have a fantastic energy as a live performance. If you get the chance to see them at a festival or something (I think they're playing Reading/Leeds?) then I strongly recommend that you do.