i'm not even that into RPG's like that. But one thing i know for sure is what someone said above with these open world games. the games are designed to have the entire world waiting on your every move.
like they are frozen until you make the next move. then they move accordingly. then freeze again. then you make another choice by doing X, Y or , Z. and they move again. then stop and freeze until you make the next move. sure these things are happening behind the scene but. if you want to make something really dynamic in a real world sense. you need to create a world where the player isnt necessarily the Constant, or the force that moves all other programming. You should be apart of a whole.
for instance. lets say there is war going on between 3 factions, and you are apart of another faction(big or very small or even on your own(ninja) you're a faction to some degree. The 3 other factions should be going about their business as usual. setting up their plans for global take over or whatever their plans may be. but doing so on an extreme front where its noticeable by you the player. that almost forces your hand to jump into the battle. now the question is depending on how each factions operates will help you decide which angle you are going to jump into this equation. Then things you do obviously affect what others are doing. but you are not the main character. you are one of many. you can make yourself the main character if you climb to the top of the food chain so to speak.
ex. in real life. if i'm a low level corner dealer. no one cares about me. if i own a block only a few care about me. when i own BLOCKS then others care about me. when i own an entire town/city. now i got the law on y tail something fierce(the law is a faction). i also have big boy enemies as well as little boy enemies trying to come at me. while also having others trying to side with me depending on how strong i am, how cunning they are(strategic vs just being all about war). you've seen bits and pieces of stuff like this in all sorts of games. but never where YOU are not the main character driving everything.
or never where its not a predetermined outcome.
You want a game to last forever. set a game up like that with no real end game. the obvious end game is to get on top, OR take all the bad guys down... But if the game never ends. you never remain on top without a serious fight. you never keep the city safe forever if you're on the otherside. there's always a constant and living world when YOU are not the MAIN character with a predestined out come.
Oh I agree, Deus ex from the very beginning around 2000-2001 was always billed as an RPG. The fact that it's a 1st person shooter is simply it's method of presentation. 
............
...wrong konami game 
