re: Metal bands that did not get their due.

Accept
Anvil (Even without the documentary)
Armored Saint (Good call)
Crimson Glory (simply amazing-too bad original singer died)
Fates Warning (Invented progressive, heavy metal. Original singer, Jon Arch has no equal in style.)
Freedom Call
Gamma Ray (Probably best current power metal band going, slightly better then Helloween IMO.)
Hammerfall
Helloween (Not sure if underrated. Considered the godfathers of power metal in the metal scene but most casual fans aren't familiar with them)
Holy Grail (Cool new American metal band)
Kamelot
Kiler Dwarfs
Lizzy Borden (Take away Lizzy's theatrics, and still great music)
Metal Church (pioneers of thrash early 80's)
MSG (Schenker, enough said)
Primal Fear (Just listen to them. Ralf Scheepers. Rob Halford clone.)
Rainbow (Blackmore. Dio. Enough said. Practically invented fantasy power metal)
Riot (Mark Reale, guitar genius. RIP)
Savatage (Early albums 10x better then the later, operatic ones)
Saxon (NWOBHM and still going strong)
TNT (Probably the best singer and guitarist combo in metal, Tony Harnell and Ronni LeTekro)
Triumph (Best Canadian power trio since Rush)
Westworld (Obscure 3 albums by Tony Harnell and Mark Reale. Just about perfect.)
Y&T (anything but Summertime Girls earns them on this list)