My players don't mind conditions that add tactical complexity, like slowed or prone or something. They force them to make tough choices, and while they often have resources with which to counteract those conditions, those resources are limited, so they make things more strategically interesting. They also add a lot of flavor to monsters. And for their part, the players enjoy laying these conditions down on the monster.
Its conditions like Stun which remove tactical complexity that drive them bonkers. "You would normally get to do interesting stuff, but now you can't." Isn't a fun complication, it just blows.
Once in a blue moon, breaking out a stun for a round can be useful. Its an "oh crap" signifier--if the monster drops a stun, they know he means business. And most players can handle losing a round here and there without it destroying their fun.
But stunning auras, at-will stuns, or multi-turn stuns? Just suck. I won't use them, and I prefer my player don't either. The save-ends stacking orbizard who drops sleep (even with the nerfs, can still guarantee like 2 rounds of failed saves) is an outright encounter destroyer.