Volume 6 of the Essential Fantastic Four brings the Stan Lee era to a close, and he was a tough act to follow. After all this was the book he used to launch Marvel Comics into the entertainment empire it has become. Without his influence the book quickly entered into a period in which its identity was lost.
Lee was followed by some fairly notable writers, Roy Thomas, Archie Goodwin and Gerry Conway all have stories in this volume, and the great John Buscema is on art for all but one issue (although it's not up to the standard of his Avengers or Silver Surfer runs). But for some reason none of them really know what to do with the characters. Wisely they all reject the passive role the Invisible Girl had played up until this point, but they way they resolve this is to progressively turn Mr. Fantastic into a bigger and bigger chauvinist until she finally walks out (to be replaced by Medusa). The introduction of Thundra (a seven foot amazon who constantly rants about the weaker, male, sex) is an equally heavy handed attempt to address the wrongs from the first hundred or so issues.
But given the amount of issues in this collection and the talent involved, there is certainly some good in here as well. The Human Torch, Crystal, Quicksilver love triangle is a definite high point. The introduction of Air-Walker, the second Herald of Galactus is quite good too. But it's hard to deny that the FF were treading water at this point, and pretty much continued to do so until John Byrne came on board much later.