My main complains so far would be the efficiency decaying while waiting for the portal after you finish each zone this can be anywhere between 5-10+%, i had instances where we were able to keep up the efficiency up to 100% just to be dropped to around 80% while we were waiting for the portal to spawn i don't know if this is a client - host problem or a hardware issue but i guess it could be fixed by either pausing the efficiency when there's no more enemies to kill or to keep the enemies spawning so people can keep their efficiency up, another one would be weird freezes, they seem to happen