So far, it's fun. Yet to play COOP with anyone but the campaign is pretty sweet. One thing is for sure whether playing multiplayer or single player, no cover, no live.
The few online matches I have played have shown me how much tactics are needed for this. If you get a good 4 man team, shit, 2 man team who communicates, you win. Flanking, suppression, utilizing the tools at your disposal, calling out targets, it all comes together nicely. If you run out and try to take guys head on..you die. You need to use the environment to your advantage.
One thing is getting used to the 3rd person over the shoulder style. It has a bit of a wide turn radius, doesn't let you turn quick and engage. Might be different on PC, could just be the controller.