Just Cause 4 changed everything around. It's just not fun, it's really boring, plus the progression has been changed all around.
Let's be frank, the Just Cause games were never the highest of quality, the plots were always terrible, and they were super repetative. But they were good zone out and just have a good time exploring and playing action-sandbox sort of games. Just Cause 2's map was pretty big for it's time too. 2 and 3 are the best of the series. 4 is a dud.