Masterpiece status probably goes back to the originators but not exclusively of course. The issue with masterpiece status is you've heard the album so often its ingrained in your DNA. For me Brain Salad Surgery is a masterpiece. So is Close To The Edge, Selling England By The Pound, Of Queues And Cures, and on and on. I don't need to hear them again. They are a part of me.
There are more recent albums like Riverside's "Out Of Myself" that for me is a masterpiece. Zero Hour "The Towers Of Avarice", Spiral Architect "A Sceptic's Universe".
A great album is one that as a whole you get incredible enjoyment album - even if there is a weak track hiding on the album. A masterpiece is one that is near life-changing. It shakes you to your core and resonates with you on an emotional level. Its the one you don't have to discuss with your friends because they already know.