Unlike but akin to Hidden Gem, a Buried Gem is a piece of media possessing great value and quality, however it's hidden or buried under something that easily overshadows its presence.
"Hey bud, have you ever heard of Pokemon Adventures?"
"Pokemon? Pretty sure everyone in the planet knows what that is."
"No, I'm talking about the Pokemon Adventures manga."
"Pokemon has a manga? Is it like the anime?"
"See, this is why this series is a buried gem. No, the manga is a direct adaptation of the games. The themes and visuals of the story can be much darker than the rest of the Pokemon franchise, but in its core it tells great Pokemon stories containing tons of heartwarming and wholesome moments."
"Sounds interesting, I might check it out later tonight."