I started gw2 about 8 months ago and fell in love with it almost instantly. The art style is amazing, and makes almost any view look like a painting of sorts. But what really sold me the game was exploration.
I was mining my first ores in a cave in Caledon Forest and saw something weird in the corner. I climb up and find an opening, through which I enter a huge cavern filled with lava, golems, floating holographic platforms and all that. (first time seeing Asuran tech/buildings) I just stood in awe for a minute before doing the jumping puzzle. The area wasn't on map and it was glorious. The fact that the game manages to give me this feeling of discovery in every zone over and over again is astonishing (and somewhat addictive).
I do have to admit that the core game's story was underwhelming. But by the end of Living World Season 2 I was hooked already. Oh, and I couldn't play the game without action cam (activated in the settings).