(Author's Note: This review was written when Just Cause 4 came out; I've not played it much since then. It's possible the issues addressed by this have been dealt with.)
Started playing Just Cause 4 tonight. It's... pretty damn buggy right now. I'm also not a huge fan of the direction this game took in terms of completions; instead of random rampant destruction (which the game still insists you do, by the way, it just doesn't seem to count any of it save for chaos), in order to complete a given location, you're tasked with completing things like stunt challenges. Which, I mean, they're fun, but the whole reason to play a Just Cause game is to fuck around and do your own stunts, not do them because The Man insists you do. (Or the woman, in this case. Long story.)
They've seriously improved car handling since 2, but at the detriment of motorcycles; in Just Cause 2, motorcycles were by far the best vehicles in the game because they drove fast (some of them, particularly the Yahama models) and handled like nobody's business. You could turn on a dime riding them. Meanwhile, in 4, you try to turn and immediately start fishtailing trying to retain control. Which I guess is real enough, but realism isn't why one plays this game.
My biggest complaints thus far involve the AI, particularly in driving and enemy handling. While driving, of course, you tend to speed past everyone else because you're playing a damn action movie; in past titles, this was handled by having vehicles cautiously move towards the side of the road as you approached, in order to get out of your way. In this game, AI drivers swerve, and if you happen to be turning while staying in your own damn lane, oncoming traffic makes the assumption you're turning into their lane and swerves directly into you. In a game where one metric is literally "how long can you drive at max speed?", this is game-breaking. You could be going 300km/hr in a sports car and be brought to a dead stop because some damn auto rickshaw pulled into your lane in a misguided attempt to avoid you.
The AI for the enemies is fucking terrible. Best example I can provide is another while driving: for some dumbass reason, the Black Hand (the "bad guys" in this game) were driving a literal tank on a major highway; this was not part of a blockade or anything, just crazy random happenstance. In trying to pass it, I nudged the tank, not even enough to register damage to my own vehicle. They literally that moment immediately called in air support, and I had about five helicopters all firing missiles at me over a light brush. (Meanwhile, I steamroller literally dozens of citizens with an Indiana Jones boulder, and nobody bats an eye.)
It's not a bad game, and in most cases it's pretty damn fun. I just, it's super obvious they haven't really finished it.