well, i dont know to much myself but i know that human revolution is a prequel to the other two so if you are new to the series than this is great chance to enter into the series. The games are a mix of fps and rpg sort of like borderlands. I have played a little of the first one and enjoyed it and this third one is going to be similar
Deus Ex- Betrayal. Conspiracy. Terrorism.Augmentation.
Deus Ex Invisible War- Conspiracy. Terrorism. Augmentation. Depression. Controled Society.
Whats great about DE:HR it's like MGSE, you don't have to play the previous games, to understand it.
Deus Ex my all time favorite PC game and one of my favorite games ever. If you love conspiracies, DE is your game.