IDK if I'd call it a gem, buuuut Styx: Master Of Shadows on was a fun surprise for me. It was a free PS+ game in summer 2015. I was rolling my eyes pretty hard at the opening movie that explained the lore, introduced Styx, ect, but I got into the game play itself fairly quickly, and the story eventually got pretty good too. Honorable mention to Hyperdimension Neptunia: Action Unleashed on the Vita. Charming characters, sometimes genuinely funny writing, beautiful clean graphics, and although it's a hack & slash, it never got too stale, even during the plat grind.