I started playing it knowing it can be addictive and simply decided to play it casually. I started when it came out in Austria and am still level 35, soon to be 36. As long as you keep in mind that the "achievements" you make in the game wont actually impress anyone in real life and only make the peer players jealous, you're good to go. I simply play it a few hours per week and see it as quality entertainment and from that perspective it's really nice.

So if you have enough discipline to work when work needs to be done, and be a hero, a wizard or a rogue in your spare time, I don't think it should be a problem.