Far Cry has always lived and died based on the world it presents to the player (and the antagonist since FC3).

In the case of 4, setting the game up in the Hymalayas was really inspired, it really helped visually differentiate the game from its predecessors, which featured tropical islands and a war torn African country.

Thematically, they did do a huge callback to 2, since both games feature countries which are in the middle of civil wars, even adding Longinus to 4 to bring the point home, since he outright says that he was involved in the war from 2. They also showed the whole angle of both sides of the war ending up as bad for the country, because (spoilers beyond this point) the state either remains under Pagan, becomes a theocracy under Sabal, or a drug state under Amita.