I think people don't realize how polished GW2 was even a year ago. Of course they are still adding more stuff like extra skills, dungeons etc, but the core system is almost perfect. This is a very important thing because more stable and robust your engine is, adding new content becomes easy and the speed is only limited by your artists/level designers and not coders who have to patch everything together. It means their developer tools are rock solid.
Yeah.. sometimes I think I'm more in love with Anet than GW2 ;P. It's just as a developer I love to observe things coming to live and Anet is doing it with a style.