I've been playing the game off and on whenever I have the time to, and simply put, it's one of the most immersive RPG's I've ever played. Surpassing Human Revolution was a tall order I never had on reserve for Eidos, and they not only surpassed my expectations for a Deus Ex game, but for an RPG of any sort.
The first real side-quest you encounter embodies this: the hubworld of Prague is locked and quarantined Casablanca-style, where papers and ID are essential for getting around. You can either bribe the guard, or see a forger of ID papers. When you find the forger, another optional, story-rich side-quest opens up for you to help her with her operation. Along the way, one of the oppressed citizens of Prague that's already an asset to your current side-quest will lament an extremely well-written and immesersive situation for you to help him out of, which will extend the side-quest even more. None of these dialogue sequences or characters in these labyrnthene side-quests feel formulated like the kind in Skyrim. EVERYONE in this hub has a story and a personality, one you can choose to ignore or, if you're like me, plunge into to see just how far the rabbit-hole of the writers' boundless creativity really goes.
And that's just the first side-quest of the game. It's simply awe-inspiring how dense, life-like, lore-filled and immersive they've made this in-game world, and really stomps on the empty and lazy approach to open-world games that's the craze in gaming nowadays.
The world of Mankind Divided is smaller, and yet 1000 times more detailed, intricately-crafted and immersive than any open-world game I've played in the last fifteen years.