The Elder Scrolls IV: Oblivion

The Elder Scrolls IV: Oblivion is an action RPG, a part of The Elder Scrolls series, which follows TES: Morrowind and proceeds TES: Skyrim. You take on the role of a hero that needs to stop an ancient cult from opening gates in the demon world called Oblivion. Your character is completely customizable: the game features multiple human and anthropomorphic races to choose from, different skills you can obtain and develop and abilities to improve through the game. The specification of skills you choose will affect your playthrough: the character can be more efficient in melee combat or magical abilities as well as stealthy complete some quests.
The game is set in an open world, so it's up to you whether to follow the storyline or focus on numerous side quests. You can explore the world of Oblivion freely on foot or use the fast travel system that allows moving instantly to every visited location. The game doesn't stop after completing the main story and lets you explore the world as long as you want.