Also remember that Metallica, for lack of a better comparison, are more or less something similar to the metal Beatles - although they didn't invent the genre (and so didn't the Fab 4), they codified it in the eyes of the general public and they are definitely the metal band for many people, they have a brutal appeal (even a melodic one), they took risks and progressed a lot throughout their career (more than most bands in this very cup ever thought about), people know and do care about every single individual who played there, they used to aim really high (the first 4-5 albums are brutally ambitious, if you look at it honestly) and their overall importance to not just one subgenre, but to metal as a whole is absolutely huge (and now I'm talking again also about how known they are and how popular they made the genre - yes, Sabbath and Priest are more important as pioneers, but remained in a niche market, so to speak).
(don't take it too seriously, I could make the Fab Parallel even with Ozzy-era Sabbath - for the time period and for the musical sensibilites and personalities in the band, take this all with a grain of salt).
I tended to overlook them a lot lately, especially because nowadays Lars is a shitty drummer and Kirk is a shitty lead player and they're all mostly assholes and they haven't put out anything really consistent since... well, ReLoad (or maybe Beyond Magnetic). But also because of this very cup I came back to those early recordings (now with gigs from the vaults, on the reissues) and I absolutely get why they got as big as they did. The spirit, the untrivial melodic sensibility, the sense of scope - these all might have evaporated (or at least seriously diminished) throughout the years, but even a (comparatively) weaker album of the time that Puppets is I still have no problem accepting as the epitome of metal. Side A in particular, from Battery to Sanitarium, is (nearly) perfect.
I like AOB for a Bruce album, and actually even beyond that. But for example stuff like Welcome to the Pit I picked out as an example of diversity, but I personally hate the track. Man of Sorrows and Arc of Space are way too over-melodramatic, and while I like both (the latter significantly more than the former) I need to be in the mood for it.
And yes, the whole album, it's all Bruce's voice, it's all Bruce's lyrics and attitude and that makes it more of a niche piece of art for me. The only stuff on AOB that would speak to me as strongly as the highlights of Puppets is probably only Aquarius and Omega. Mainly just the former. And yes, I played Aquarius 100 times, maybe, at one time. But Battery and Master of Puppets (or Ride the Lightning, or And Justice...) I played probably five times more. There was a time when I played just Battery and Ride the Lightning throughout the whole day. And I still listen to it and it still gives me thrills.