All of them changed the game in some way personally:
Richard
Howe
Bobby Hull
Orr
Gretzky
Hasek
Roy
Lemieux
Ovechkin
McDavid
Some other player types that also changed the game, but it's hard to pick one when there's multiple guys
-Smaller / less physical skilled, puck carrying D, like Coffey, Bourque, Niedermayer etc.
-Really physical, skilled D, like Pronger, Stevens, Chelios or Robinson.
-80s - 90s speed monsters, especially the wingers, like Selanne, Bure, Kariya, Gartner, Fedorov, Kapanen, Bondra etc
Might even want to add a guy like Datsyuk, who entertained while still being good on D