Castlevania: Symphony of the Night
When other games were going 3D, Castlevania remained staunchly side-scrolling (even if some of the enemy animations and clouds and cutscenes did incorporate a dash of 3D like someone experimenting with chili for the first time). Symphony of the Night managed to shake up the Castlevania formula in other ways, with a little bit of RPG sauce and a new art style. It also took inspiration from Super Metroid and Zelda, giving you new weapons and abilities like double-jumping, transforming into mist, and flying like a bat, each of which opened up new areas. Castlevania: Symphony of the Night was so influential, it's the reason for the "-vania" suffix in the made-up genre: "Metroidvania." Sure, it's the ugliest genre name in video games – and that's counting "MOBA" – but you can't blame Symphony of the Night for that.