What did it for you guys? And still does?
Art and forward looking design.
Art of Guildwars 2 is exquisite. Daniel Dociu, iirc, said in early design days of GW2 that the art team wanted to give character to the environment of the game. They succeeded in doing so. I'd build my home in the Lornar's pass if I could.
Many people will say GW2 is extremely casual and lacks "hardcore" content. However, definition of the term hardcore is quite varied and changes dramatically depending on who you ask. I think, GW2 design primarily caters to a crowd base that is past 25 and can rent their own cars. I think ANET will gradually add harder content but, only slowly so that people starting the game will not face a high skill floor and feel rejected. The design moved away completely from a pre-defined structure of healer, tanker and damage dealer and embraced the true essence of action RPGs where the hero can do it all in varying degree. I think, GW2 design does not look back much but, fooks forward into 2017+.