In Hearthstone player communication is strictly controlled. The six things you can emote at your opponent are: Greetings, Thank You, Ooops, Threaten, Well Played, and Sorry. At first I was surprised that people couldn't talk to each other directly but after a few moment's thought I realized that allowing opponents to talk directly would be a disaster. While there are definitely some conversations that would be fine, there would be far too much "You suck you lucky ass noob go kill yourself for playing that mindless deck" and far too little of "Hey, do you run 2 Brawls in that deck, or 1? I can't seem to decide which is best."
The funny thing is that these basic emotes end up being used to mean all kinds of other things that might not be intuitive at first glance. Greetings usually is used at the start of a match as a polite hello, but it also can be something like "Hey, check out that gigantic threat." from either side.
Thank You either means "Well, you sure did play into my trap there." or occasionally "My face got wrecked, so I might as well say thanks....?"
Oooops is a simple one since it just seems to mean Oooops.
Threaten I rarely see used, I suspect largely because the threaten emotes are pretty laughable. Mostly it seems just to be there to pass the time.
Well Played though, now that has two extremely polarized meanings. It is either used as a term of respect to mean "You played that match well, and deserve respect" or even a simpler "Good game." However, just as often it means "You lucky bastard, you did NOT deserve that."
Sorry rarely means sorry. It seems to be used to say "Well, I sure did have the right answer, so this is where you get blown out." Occasionally it seems more like "I drew like a lucksack, so you lose. That is how it works!" or "Hah hah, RNJesus hates you."
It is odd how people seem to have consistently settled on both these alternate meanings and how often emoting is acceptable. In all my games I have only met one person who emoted constantly and in an annoying fashion so I squelched them, but the great majority of people either don't emote or do so in a fashion that seems very appropriate.
Somehow even though these channels are very different from normal human communication we establish multiple meanings for things and social norms that percolate through the group very effectively.
It strikes me as a great solution, since Hearthstone really doesn't have a problem with people being gigantic assholes to each other and so many online games are absolutely plagued with that problem.