I consider them America's answer to Uriah Heep, another underrated band. Of course David Byron's vocals were more in the vein of bands like Queen and Sweet while the Michigan natives in GFR had that classic Motown beat.
Listen to Some Kind Of Wonderful and UH's Stealin back to back and you would swear it was the same song twice. And while we're at it, was Michigan in about 1969 a starting place for great rock and roll or what. Grand Funk, Amboy Dukes (Ted Nugent), the Stooges, Tommy James and The Shondells (had like half their catalogue rise up the charts with other artists in the eighties), Seger, Glen Frey before he moved west and met Don Henley and Jackson Browne, MC5, Frigid Pink (did a better version of House of the Rusing Sun than the Animals did) plus a couple I probably missed.