At first I wasn't that great but now I'm pretty good at surviving long and using my equipment properly but what gets ridiculously annoying are the n00bs who go into an online match just to be AFK (away from keyboard) basically just standing there and doing nothing or they straight-up suck and keep dying in easy rounds. Also the n00bs who just leave the game because they don't feel like playing right at the beginning or because they died.
It's so hard to find players who actually know how to play unlike on multiplayer where every n00b can "beast" due to short time-to-kill and n00by play styles like camping.
Zombies is skill and multiplayer connections therefore it's quite obvious who got the skillz and who got the connectionz since I kinda struggle to play consistently good on multiplayer. On Zombies I'm mostly the best player in the lobby and I'm not even that good