Heart loved Led Zeppelin when it wasn't cool to love Led Zeppelin, but everybody did anyway. Heart had the balls to cover "Rock'n'Roll" in the days when Zep still stalked the earth. Heart had the gentle acoustic/raucous electric thing down cold. Heart could do the metal-funk thing better than Aerosmith.
And their ballads: well, they were delicious. Zep's ballads reflected Plant's love of a California that he imagined as Rivendell. Aerosmith's were groping toward the power ballad. Heart's - well, they're something more unabashedly pop, but Ann's vocals bring enough brassy passion that they always sound like they're coming from a rock point of view.
That's all I really want to say about Heart right now. Others have discussed the Wilson sisters' importance as female rockers, with the accent on female. I just want to point out that they rocked. No need to qualify or amplify that statement: they just rocked. And their music, from that period at least, sounds better and better to me with each passing year: honest, tasteful, gritty, sexy, real.