I am currently playing Mankind Divided and have been reading into the art direction from interviews with the art director. I just love the world they have created and the way they utilize it to tell the story. One of their ethos is "show don't tell" and you can see they have really taken it to heart. The locations tell the story just as well as the dialog does.
You simple cannot compare Deus Ex 3 and 4 with Deus Ex 1. Deus Ex 1 is a much different and better game, a lot of thought went into it, the player can do so much more it's not even funny. No other game with Deus Ex in the name comes even close. Play Deus Ex 1 first and come back later, though some may never get into DX1 because the graphics hasn't aged that well.
I have played all 4 and loved each one, the charm and freedom of the first may not have been reached with it's successors but I feel like 3 and 4 at least really were fantastic games in their own right.