No deal breaker I can think off. Looks are not so important to me.

To be honest, and I know many don't think about that in the first place, but often regret spending time on a game later, is the community. A poisonous community kills my fun fast. Ingame you can shut a chat off, but a hostile community in the forum kills the game. Overzealous game admins can do that too, but that is a whole other story.

Now I think of it, an overactive PvP community can kill a game too for builders like me. I want to build cities without dying every day.

I can't stand MMOs where the majority of players can't speak English. This pretty much writes off any MMO made in Korea or Japan without massive popularity among English-speaking countries.

It's a problem with communication mostly. I like knowing what I'm told to do in a group.

In the past I must admit I am one of those players that spends some time with the Creation even deleting them soon after creation when they look differently in game that in the creator. Even though I look at their back or butt for most of the game it is still nice to have a nice face to go with it. However with CoE where you die every year I am not sure I would spend that much time on creation this time around. I think I can mainly get the hair and eyes roughly where I want them, find the girth that is acceptable I feel I would be ready to go.

None of this is a 100% dealbreaker but all this things disapoint me in games, not only mmorpgs

Spetacular Atacks with lots of lights and particles, if the Lv1 basic magic atack is a backflip+hadouken+aura explosion i know that probably the game is not for me. If the "magicless" characters have atacks with lots of lights and particles... i'm probably not going to play.

Bikini Chainmails 2 simetric oposed factions wagin war against each other for whatever's sake Gigantic/desprportional weapons UI with a gazzilion of things, the cleaner the better imo... Absence of capes and mounts in medieval games

Luckly, it seems that CoE won't feature any of these

Idle animations. Try to roleplay a serious character while your avatar randomly bounces like some cheerleader.. (nightelves in wow) bleh, hate having no controll of own characters doings.

Emotes are easier to avoid if not to my liking but can become annoying as I like visuals in my playing, not just text or bad ones..

When devs cave to casuals wanting the game to be changed to being easier, thus removing challenge from the game (also happens to remove the game from actually being a game, because part of the definition of "game" is to overcome a challenge).