I owned their first four albums (the last one I bought was their double-LP live album). I think their debut is one of the best rock albums of that period and holds up well today. "Cold Gin," "Black Diamond," "Strutter," and "Deuce," are all excellent hard rock songs. Their next two albums, Hotter Than Hell and Dressed to Kill were not anywhere near as good (loved the back and white cover of Dressed to Kill, though), but they were okay. By Dressed to Kill, they had almost started to parody their image as studs who would fuck every plaster caster who would venture backstage. Everything went to shit when they cracked Top 40 after the live album came out when "Rock and Roll All Night" went monster hit on them.
I saw them live in 1974 or 75. Believe it or not, they were top billed with RUSH! Rush were on their Fly By Night tour. Geddy Lee had bad laryngitis and could only sing for about 30 minutes. Kiss came on stage and rocked it. Despite their theatrics, they were (at the time) a great band (kinda like Alice Cooper from their Killer, School's Out, and Billion Dollar Babies era). But yeah, their debut album is the only one worth getting, IMO, and "Strutter" is just a killer song, as is "Cold Gin."
I think, in some ways, Kiss' success went to their heads just as it did with Blue Oyster Cult. I was into BOC right out of the gate and I consider (like many fans) that their first three albums (BOC, Tyranny and Mutation, and Secret Treaties) represent their very best work. By the time they released Agents of Fortune, like Kiss, they hit it big on Top 40 with "(Don't Fear) the Reaper," and, IMO, they started to decline. They had some decent music after that, but nothing topped those first three releases...what a crop of songs: "Cities on Flame with Rock and Roll," "Before the Kiss, A Redcap," "Flaming Telepaths," "Astronomy," etc etc etc.