To build an atmosphere you need a scripted scene, mood music and a known outcome.
If you are trying to build atmosphere and I suddenly run down a different road into a field, then start to climb a buidling for no particular reason then the atmosphere is instantly killed.
If you are saying you want a hybrid game of open world and scome scripted on-rails elements then fine, but thats a different genre.
That's not what I mean. Out of mission it's very hard but in mission atmosphere in assassin's creed is so lame. They could also improve special effects and things like weapon effects. The order mastered this. Kinda hard to play other games after experiencing it.