Calling a game 'addictive' is a playful compliment. Let us not mistake it for a serious assessment of the situation. Games do not foster physical dependency; they do not coerce the player to chase a diminishing high until his whole life is a ruin. Except WoW. ;)

I think addictive games come in two flavors, one negative and one positive.

The negative type are games that don't let you go, that you wind up playing long after you've lost interest in them. Games that are centered around a guild that needs you, so your friends draw you in. Games that must be played regularly and so form habits. Games that threaten to punish you severely if you don't frequently check in. This is a negative sort of 'addictive' gameplay: it eats up time, demands attention, serves as a second job. Games like these should be enjoyed briefly and then escaped from. Lucrative though they may be, I would not want to develop one.

Then there is the positive sort of 'addictive' gameplay, which I might call more accurately 'fascinating'. These are games that dazzle and delight, that eat your brain, that you wind up playing for 16 hours a day for a week because you can't stop thinking about them. Like a fascinating problem or a motivating vision, they push you to perform and learn. This sort of addiction always dies out eventually, but while it lasts it is enjoyable and rewarding. I would go so far as to say it's what gaming is about. Yeah, it may cause the occasional day of missed work, but it gets the odd hacker in a serious groove, too. I think games with this quality are excellent and even make the world a better place. I would strive to make any game I built so 'addictive'.