So far I've just gotten perhaps 15 percent of the way through. From far cry 4 there's a significant step up. I love the dynamics of the bullet trajectory and how realistic the guns are, for example the assault rifles bullet drop is at a significant distance where the sniper variant is the same weapon with a longer barrel, and the bullet drop kicks in way later. The attention to detail and the fact that guns sound like guns is great! Far cry 4 had very poor audio for gunfire, clearly not the issue anymore.
I love the customization of the characters as well as the guns, the variety of guns isn't a vast one but the selection of guns that were chosen for the game is excellent! Don't think I'd use anything other than these to be honest.
However the missing 5th star falls to the fact that I'd like to see a few heavier gunfights where there were more enemies at once and you'd have to really put your guns and aim to the test to get through, not to say that the actual encounters aren't absolutely fun and challenging. The games got a great rpg feel to it and the playability is tops. Definitely my favorite far cry so far!