Just Cause 3 is what I would point to as an open-world game in it's most purest form; The only thing expected of you in the game is to fly around and blow s**t up. Oh yes, there are technically story missions, however there are not all that many of them, and they never take themselves seriously. They are all a tongue in cheek, way over the top ridiculous kind of humor that shows that the developers or story writers knew that the whole premise of the game was ridiculous and they fully embraced the fact that you were about to go tether onto a flying missile and control the thing.
So what is good about this game, and what is bad:
The movement in this game is down right phenomenal. There is simply no better game in existence that has ever gotten the simple act of going from point A to point B to be so damn fun. The tethering, the wing suit, the tethering with the wing suit, the powered wing suit, the vehicles, etc. It is the only game where I have felt like a superhero just by flying around and doing nothing in the game. This should be the gold standard for movement systems in games, hands down.
The vehicles are fun and easy to get. This is a game all about blowing crap up, and finding unique ways to do so. Having the ability off the bat of spawning in a helicopter to hang off the underside of as you rain down RPG's is the right approach.
The graphics are really fricken good. It looks beautiful, driving through a lavender field and seeing your tracks behind you in the sunset on a mountain hillside is a cool feeling.
The gunplay, while not great, is far from bad. It does it's job, and it does it pretty well. the variety of specialty weapons however is a highlight of the game, from the most powerful bavarium nuke launcher type thing to the cool grenade launchers, It has enough weapons to keep you entertained.
Now lets talk about the bad:
The biggest problem this game has is the repetitiveness of the enemy bases. There are some really fun and cool ones, such as the air base on the mountain, or the mining base with these huge digging machines, however a lot of them were the exact same copied over, and didn;t encourage unique approaches to destroying them.
The second biggest is definitely that they use denuvo. This is a horrid DRM that hurts legitimate buyers of the game, and there is no excuse for why they would force it upon consumers. The team who worked on the game must hate it too, because the enemies are called D.R.M.
This seems to be a reocurring joke amongst games.
Other than that, there are very few problems with the game. It is repetitive and lacks diversity, but other than that there is not much to say. While the game could have been so much more, they had a vision and created a game that accomplished that vision in a well polished way, and that is more than most games accomplish these days.
In short, this is GTA if it was boiled down to just blowing stuff up and driving fast cars, if it were polished and made more fun.
Overall it is definitely worth the buy, on sale or not. If you wish to make a semi-political statement about DRM, do not buy the game, however this is a game that it might be worth looking past your morals so that you can enjoy a great product.