Pros
Art team is good and you get to work on interesting concept stuff Design team is decent, you get to work on fairly interesting stuff as well
Cons
Arenanet is risk averse and tries to avoid any technical challenges. This means you will learn nothing important here as a coder. Especially because Mike O'Brien is very hands on with the coding department. They also don't care about your growth as a professional. Not only do they not care about your growth, but they also don't pay much. Basically they try to be a low tech risk-averse company in terms of software engineering. MMO industry as a whole is a subniche of a niche that is gaming. MMOs are addictive and exploit players, sinking enormous amounts of their time without any human message, grinding the levels. While GW is not the worst of MMOs in this respect, it's still a massive time sink of a game and NCsoft parent company is quite comfortable exploiting players with basically borderline porn (Blade and Soul). Generally speaking working in the game industry as a coder is a poor choice of skillset for investment of your time. You only live once and every year counts towards the skillset that you build. Working at arena will not improve your skillset in my opinion.