Currently nearing the end of BioShock 1 from the collection (Awesome game but for another thread). Don't want to jump straight into BioShock 2 to advoid fatigue so I'm thinking about what's next and getting into the Deus Ex series is lookin like the move, especially since until tomorrow morning, the Delux edition of Mankind Divided is 6 bucks :0. No brainer buy, but I have not played Human Revolution and dont wanna be lost.  

If Metal Gear Solid and Kindom Hearts is like 10 in must play predecessors to understand plot and Assain's Creed Odyssey is like a 1; how would yall rate Deus Ex? 

The story itself isn't very complicated to follow. I would say it's okay to play the newest one without playing the others. If my memory services me right, there is a "previously on" when you start the game. If I'm completely wrong, you can always watch a video on YT about the last game to catch you up.

You could just play Mankind divided if you really wanted to, but Mankind divided takes place almost directly after the ending(s) of Human Revolution so the set up of whats going on and why its going on is something you might want to see first hand. Also the main character Adam Jenson is the lead of both games so it might be good to play Human Revolution so you can get acquainted with him, though pretty much every other character in human revolution doesn't make an appearance in mankind divided. Also many people think Human Revolution is the better game.

You would miss a lot. Be pretty pointless to play MD without playing HR first. Not just story but connecting with Adam Jenson and his world and the people in his life.

They only Deus Ex game that you need to play is the original with the HDTP mod.