The daily reward system. There, I've said it.
One can complain about time-gating, about checklist wars and so on - while this may all be true, personally I find that this helps me maintain a healthy attitude towards the game. If I only have little time available to play, the game offers me a quick way to still make some progress through the daily rewards. If I have more time available, I can make additional progress, yet to me there will always be that one point where I think that I'm done for the day, because I'll much rather return another day when I can again benefit from the additional rewards.
To me, this is a refreshing experience. In other online-games I played in the past, I often felt like I had to continue for yet another activity and yet another and yet another...
That aside, I also like previously mentioned things such as the wallet or the pretty graphics
Commenting on the OP:
Seriously, how can any MMO still have "first tags" on kills? I'm so used to just getting credit for killing stuff that when in other MMOs I don't, I think it must be a bug.
I would have wholeheartedly agreed with this a few months into launch, however, recent changes to the game made me feel like it's moving away from its originally clever implementation.
First of all, there is spawn camping. The most obvious one are the champ trains. There is even a damage-competition, which means that not necessarily everyone is sharing loot. The less obvious places for spawn camping would be the "revamped" world-bosses such as Tequatl and Wurm. Due to the current overflow implementation, you'll be camping these spawns if you want any real chance to successfully complete the event.
As far as sharing loot goes, I've already mentioned it above: While near-perfect, the champ-trains somewhat left an ugly dent.