This is my choice for game of the generation for the reasons below:
It is an overall package that offers high quality throughout its gaming experience.
Two top tier expansions.
Great and memorable soundtrack.
Gorgeous art direction that still look good.
Sold very well.
Single player game with no online components whatsoever that is still being talked about daily.
It inspired a TV-Show because of its success.
Huge cult following and is constantly being compared to every new big release, so its some kind of a gold standard for open world games.
Holds high ratings and numerous gaming awards universally.
Available on every gaming platform with good support.

This single game made a small developer like CD Projekt Red into what it is today, this game was an industry changer and i can easily see its influence in todays open world games and im sure it will influence future open world games as well.