I've pretty much only played co-op since getting the game. Dabbled in PVP a few times, but I can sink hours into co-op.
Hardcore co-op is fantastic on a good server with people communicating. But the lethality of the bots can be incredibly frustrating. Sometimes the bots exhibit behaviour which from a human player would be obvious hacking.
I don't mind challenging AI, but sometimes, this can be rage inducing. I was playing on a "tactical" server last night, where people are encouraged to move slowly and clear as many bots as possible before capping objectives. The map was Precinct (I think? the one in a city), I was dead (standard) and waiting to respawn, so I had to sit patiently and wait a good 4-5 minutes while the last 2 guys were clearing. They finally capped the point, and I re-spawned and began to move up. 30 seconds later, I peeked out of a window overlooking the courtyard point. There was a bot maybe 20 metres aware on the ground level walking through the courtyard. I was at his 2 o'clock in a darkened window, and yet as soon as I peeked, he saw me and fired instantly without so much as stopping to aim.
Stuff like this and their apparent clairvoyance when it comes to knowing to push
exactly as you tap the reload key, or their ability to land perfectly cooked grenades/molotovs directly in your back pocket, really suck the fun out of it. I wish they'd tone down some of the superhuman abilities just a tad - there's no satisfaction in losing to an enemy like that.
Aside from that though, the game is great. Thoroughly enjoying it after some initial reservations