Black Sabbath - Heaven and Hell
When I was 12 this album came out and I knew 2 songs on it and loved them but was not sure if I could spare my limited album money on Black Sabbath, especially with a replacement singer.
Years later for the price of a CD or 2 for Tidal and Qobuz, I can hear every single Sabbath track and realize I should have bought the album in 1980. This album is my new favorite hard rock album.