Very important I’d say, it gives backstory on both Adam and the overarching villains of the trilogy. Also Human Revolution is the better game, for all it’s quality of life improvements the story and setting of Mankind Divided just isn’t as good, probably why it reviewed lower. I just hope that the trilogy isn’t dead before it is finished with the 3rd game, Mankind Divided didn’t sell as well as Square hoped, and they pulled Eidos off of Deus Ex to work on Shadow of the Tomb Raider and Avengers. Supposedly the Deus Ex hiatus is only temporary, but we shall see. Hopefully once Avengers releases in September, Square lets them get to work on the 3rd game in the Adam Jensen trilogy, for next gen.