Master of Puppets took me awhile to get into despite how loved it is. I still hate Damage Inc. but the rest of the album eventually grew on me. I still think RTL is vastly superior though.
I agree about master, though I'd put Justice first. It's the reason I became a Metalhead, & then a general music nut in the first place, & thus it's my eternal, untouchable #1 album. Even as I've slowly fallen out of love with the band as a whole, that record still stands in a league of it's own.
As for what's grown on me, I'd say Coverdale/Page. The first time I heard it I gave it a severe 'meh' rating, but I threw it on the other day on a whim & have been wearing it out since. I wish more would've come of this project, Coverdale's such a killer vocalist. But alas, Plant got jealous, even though his initial refusal to join Page is what birthed the project in the first place.