#5 Shadow of the Colossus
Shadow of the Colossus is the second game from Team ICO, which created the previously listed game, Ico. Rather than escorting a girl throughout a series of puzzles, the player ventures through an open world upon his faithful steed on a quest to slay each of the game's Colossi—boss monsters.
Each Colossus has its own strengths and weaknesses, and it's up to the player to discover what their weaknesses are and exploit them in order to kill them. It's a lot easier said than done.