In terms of ranking KISS albums I think I'd actually put the Ace solo disc over Love Gun. Mainly because Ace didn't do an unnecessary cover of 'Then She Kissed Me'. But then again 'Wiped Out' is probably just as bad from another direction.
This retrospective has convinced me that "Then She Kissed Me" is the beginning of the end. Rock and Roll Over is uneven, but there's nothing on there that says, "this band is over." Love Gun has several standout tracks (I'm partial to "Love Gun," "I Stole Your Love," and "Almost Human"), but self-indulgence was what was going to destroy KISS.
So you go from "Then She Kissed Me" to Side 4 of Alive II, where they don't play on each other's songs. Then the solo albums - maybe the most self-indulgent thing a rock group has ever done. Ever. Even counting all those concept albums. Then you have Dynasty, which is just an absolute damn mess (and the album that these reviews most changed my opinion about).
Then you have EuroPop (or whatever) on Unmasked. Then you have The Elder, fueled by Bob Ezrin's cocaine addiction. The Elder is terrible, and is rightly reviled as one of the worst missteps in rock history, but people forget that it was already over at that point.