Guild Wars, Guild Wars 2, both great games. Other than a brief stint with The Secret World, they're the only MMORPGs I've been able to play to endgame without getting bored.
If you have a PS4, consider checking out Battleborn and No Man's Sky when they release over the next few weeks or so.
And if you haven't played The Witcher 3 yet, I'd go for that game first. It's single-player, but it's got an expansive world that MMOs would kill for ... and its story, gameplay and art are so, so good.