Good in story, not so much mechanically
One main reason to get this game is the campaign. It is fun, and a lot of the characters are enjoyable, if only for their ridiculous and fun to watch actions. This is a co-op campaign with at least 15 solid hours, give or take an hour or two depending on if you're playing with a friend or you use certain exploits in levels. The campaign is definitely strong up until the end, which feels rushed and not nearly as satisfying as some of the earlier levels in the game, not to mention most fights can and probably will be quickly won using rpgs or a melee glitch for one of the final bosses. The bosses prove to be of very little challenge, and really show that this game doesn't have the right type of gameplay for bosses, as these types of games usually don't.
The characters in this game are enjoyable, for the most part. This game does feature character customization, and the character you create will be put into the game's cutscenes with the voice and outfit you've chosen. While this is great and all, there could of been more options for voices, and clothing options don't go as far as they should have. The enemies in this game are enjoyable and fun to watch, but they really fall off towards the end.
The open world aspect of this game is very cool, the music options are nice but could be more varied, and the side missions are somewhat enjoyable but can be a massive drag with some mechanical issues, and once again the game proving that these types of game's gameplay doesn't work with certain types of fighting. This game does slowly give you options for different fighting styles, which are fun to use but could use more variation.
This game is glitchy. It is a guarantee that at some point a glitch will force a restart. The side missions are too long. Anything can be bad when there is too much of it, and many of these missions can feel like nothing more then an achievement, in the sense that you're only do it to get one. There's usually nothing wrong with that except when it's done like this. There are many different side missions that have 2 sets of 6 that have to be completed. Money is necessary, but these are hardly worth the time.
The end doesn't feel satisfying. Instead of killing one of the main three bosses that have been a pain in your ass the entire game, you end up in a helicopter section that could have been a lot better. The "level up" system in this game, which it really isn't, has no real purpose in being in the game. It's suppose to make it so that you have to play side missions to be able to do story missions, but this almost never comes into play, if ever.
This game is not as good for co-op as it should be. Co-op either makes the boss battles ridiculously easier than they already were, or it makes some of the missions just unbearable. It it inevitable that at some point during a co-op campaign one of you will go down while the other is too far away to get you, leading to a most likely infuriating restart.
Lastly, there are various mechanical issues that get in the way, and these are noticeable from the start, but not enough to detract too much away from the game.
Overall this game is good for its campaign and sort of its open world, but it is definitely not the best in terms of co-op. I would definitely recommend a rental first, and then a purchase if you feel as though the game has more to offer than what I wrote.