The phrase "to play this gem" means to experience or engage with something that is considered valuable or special. It usually refers to appreciating a piece of music, a game, a movie, or any other form of art or entertainment. Full definition
I do miss co-op in the campaign, but I am having so much fun playing this gem of a video game that I am willing to give it a 9 out of 10! (metacritic.com)
If nothing else, it's great to play these gems with trophy support. (playstationwire.com)