I mean, it's Deus Ex - do I really have to say anything else?

The father of the immersive sim genre, right next to Irrational's System Shock 2. An engrossing story that's just as reactive to the player's actions as the gameplay is - not to mention its "Best of All Time" quality soundtrack from Alexander Brandon, Michiel van den Bos, and Dan Gardopée.

If you haven't played Deus Ex already, you absolutely should - it still largely holds up nowadays, just make sure to download Kentie's Deus Exe Launcher first. And if you have played it before, then you're probably getting ready to play it again - you might find something you still haven't found yet.