GW2 is like the Minecraft of MMORPGs. It's age is irrelevant, you never finish, it's just as fun solo as it is with others... I will never get tired of it. The base game being free feels like charity.
My favorite parts are 1, how customizable your characters and skill sets are, and 2, how much there is to explore. There's so much room for self expression, And after many years on my character I've still only seen 30-40% of the map.