The Witcher 3 hands down is the best game I have ever played in my life for various reasons:
First and foremost, the brilliant series of Novels this game was built upon which gave the game the most powerful and dramatic story I've ever seen in a video game. The storytelling was consistent and amazing with a great deal of different characters, amazing plot twists, vast world with different races, realms, and creatures that fight, thrive alongside one another and coexist in the most bloody and spiteful way.
Secondly, the gameplay was precisely implemented to exploit the witcher's abilities and to test the players' approaches and playing styles.
Thirdly, the choices and their consequences. This was a brilliant way of approaching the game by basically saying that there's no moral high ground here, you are a person who has trade. a traveler who is traveling along the journey and got to make choices that will benefit you and faced consequences.