Alienation does have couch co-op, for those asking.
https://youtu.be/6CTZ6KoAOYY
Replayability was really high for me due to the different classes playing out so differently, plus I wanted nothing but Legendary gear with max slots on my characters, which will take awhile to farm as it is the most rare loot in the game.
They patched in color customization for armors (with different perks), and increasing rank allows you to change ammo color too. Its possible to view enemy models as well for those who enjoy that, and there are pretty tough UFO missions after you complete the game (beware that if you die in these youll need to find another key to access the UFO). You can also go back to previous levels anytime youd like if you feel youre not ready to move on to the next level.
If youre interested in putting in the time to go around entire maps destroying checkpoints, you will be rewarded extra loot boxes at the end of levels. I think the limit is 4 though? I only recommend doing this after youve completed all the objectives since its risky. Enemies will respawn if you die, so think twice before you do this.
The game gets brutal in harder difficulties but the rewards are higher.