1. No Stories
I play RPGs for the stories. It's not the only element, but it's the most important one.
Guild Wars 2 doesn't have stories, other than a single main questline (which is not particularly well written). All the hearts have terribly simplistic situations, with simple resolutions. There are no interesting characters, no twists, no plot other than the vaguest semblance of one.
There were 17 quest hubs or hearts in the first human zone. I don't remember a single one.
2. The Grind
Go to a heart. Kill or click on stuff until the bar is filled. Go to the next heart in order of level.
I just don't find this process interesting. The events and main questline do break up the monotony, but it's not enough. It seems extraordinarily linear to me, without even a decent story to make up for it.
3. The Combat is Bad
I don't like combat in GW2. It's boring and involves a lot of waiting for cooldowns. It's also very fiddly with all the long cooldowns. It just doesn't feel visceral or fluid.
Even the touted combos are boring. Someone put down a field? Click your finisher ability and random stuff happens.
Now, I can see how someone might like this combat. It has the potential to be very strategic. But I prefer a more immediate style of combat.
4. Character Models and Animation
I don't like the character models and animations. They simply do not look good to my eyes. All the models feel like there is something wrong with them. Especially the human models with their matchstick legs.
Now the environment and other effects are very nice. But not the character model which is on-screen all the time.
5. Playing Alone Together
For the most part, the presence or absence of other players simply does not matter in this game. At most, a fight might be slightly easier because another player helped out. But even groups of players are nothing but a zerg.
In other MMOs, the presence of another player affects my gameplay. Maybe I have to kill mobs in a different area because she's killing stuff over here. Maybe I have to wait for her to finish something before I can proceed. Maybe we'll group up so things go faster. Maybe we don't and things go slower. Maybe she'll get that ore node before I will.
The other player and I both inhabit the same world. Our actions affect each other. Maybe sometimes this interaction is rough and negative, but it's better than the smooth nothingness of GW2.
I think the element that pushed me over the edge here is the fact that resource nodes exist for all players. If I see a copper ore node, and someone else runs up and mines it, the copper node will still exist for me. I suppose it's very convenient, not having to worry about other players "stealing" your nodes. But at this point are the two players even in the same world any more?
There are a few times when the presence of other players matters. The biggest is reviving a downed player. At those times you can almost see the game that could be.
Basically, I just do not like GW2. The only element I really like is the weapon and skill system. The events are okay as well. But I just do not find the core mechanics to be fun, and I'd rather play a game with interesting stories. I have not seen anything yet that would keep me playing.