Disregarding the SP mode, the horrible music, the weird framerate, and the jank, the biggest problem is that all the depth is hidden away behind actual good players. There's a very large gap between people who know how to play this game and those that don't, leading to some painful losses and salt.
I don't blame them. Most of the mechanics aren't explained. You probably didn't know you could parry the Brainer to stop all those melee kills. You probably aren't using the Jammer to use zombies as a form of finding players or finishing them off. You might even be running out into a hail of gunfire instead of playing more methodically.
The game tells you almost nothing, and throws you into the fire.
Unless you have a decent team, you are going to get bopped, and the learning curve is pretty high until then. Couple that with quick matches, and it's basically over before you can learn anything. Once you get there, it's fun, but it's a pain to trek up that mountain to see if you like the game or not.
The marketing for this game made no sense, and they certainly did not explain the game well enough. There's a stark lack of good tutorials beyond very basic things. And simple quality of life elements aren't present.
But damn, I'm glad it clicked for me, because it feels a little goofy yet intense. The last match I played, I used the Jammer grenade to mess up the enemy team camping in a house. They got swarmed, running out to protect themselves, and we picked them off. Shit like that is what makes this game so great, and kind of deep, but because the game won't tell you anything, you might not even see that.