I'm not a big KISS mark, because I adored their 80's glam phase. I thought their unmasked era was KISS, for me. Their brand of melodic, radio-ready, pompous hair-infused power rock was really the best the medium had to offer if you think about it. Because I think in some ways KISS was self-parodying the scene, consciously. Something they did with the original glam rock in the 70's, and I don't think they get enough credit. At least 80's KISS was tongue-in-cheek, unlike say Motley Crue who actually took their shit seriously.

As for the KISSalog:

I personally think for a casual, the basics are probably in order. Firstly, go grab you a Greatest Hits and see if you dig it. The "Very Best of KISS" was a good set that included most of their big-time 70's hits, with a couple 80's tracks thrown in for good measure, and locking out with the "God Gave Rock N' Roll To You II" fantastic cover.

The catalog itself?

For casuals:

KISS (1974)
-- Their self-titled debut is an absolute must, for anyone. Fans, non-fans, casuals, diehards, in-betweeners -- everyone. An absolute amazing debut, this is another debut album rock classic, no different Queen I or Aerosmith '73. The fact it's not put on more all-time rock lists, nor recognized by the KISS Army as probably their best work is beyond me. Just downright hard rock. The band at their purest imo. I adore it from their catalog, and it should be a first listen.

Alive! (1975)
-- A better compliation of their two-albums in-between of KISS '74 and Destroyer, although Alive! is seen as tame by today's standards, not to mention "Memorex before Memorex" (alot of re-dubbing), it still is a classic in rock history of live albums. Just the sound on the record, and an almost aggressive 'real deal rockers', this set shows for those who weren't there what a live force these guys were at that time and the talent throughout the band.

Destroyer (1976)
-- By this point, this was their fourth album release, but in alot of ways the first true follow-up to their self-titled debut. An absolute legendary rock classic (masterpiece is stretching it), this was released at their prime and features a slew of their memorable classics with a tone that fans so adored that the band has tried to re-duplicate it to this day. Features Detroit Rock City, God of Thunder, Do You Love Me?, Shout It Out Loud, and the immortal Beth... among others.

Asylum (1985)
-- Although this is a HUGE jump in-between albums, most of the songs contained on those albums, and the forgettable solo albums, can be seen on Best of sets. Although the sound of their unmasked period really began on the sometimes underated/often overrated Creatures of the Night (1982), the official unmasking didn't begin until Lick It Up the following year. But for a real 'album listen' that captures the band at the pinnacle of their poppiest 80's sound. Several tracks are immediately catchy, and all of the ballads are pure 80's escapism.

If you like those, at all, then i'd took a little bit into mid-tier depth albums like Rock and Roll All Over, Love Gun, Creatures of the Night, Crazy Crazy Nights, and Hot In The Shade.

If you like any of those... then i'd go for the deep stuff like Hotter Than Hell, Dressed to Kill, Dynasty, Unmasked, Lick It Up, Animalize, Revenge, and the post-reunion stuff (of which i've heard very little).

When I say 'deep', what I mean is album's loaded with fan-oriented tracks that might be a difficult listen for someone looking for instantly memorable hooks and lyrics.

P.S.
Interesting listen is Carnival of Souls, for the diehards-only, as it was a failed attempt by the final album from unmasked KISS to do a 90's-themed, darker, more grunge-ish record.