Part of it was that the world was just beautiful! I think the other part was that it wasn't fully a MMO, it just felt and played different, and the restriction of hotbars to only a few skills definitely gave it this fun deckbuilder-y quality and made build experimentation way more fun. GW2 still of course does this, but it felt like the scope changed so much and it became too mired in its own systems. I bet I could like it if I gave it a really earnest shot, but it's just not the same for me there.