Its VERY addictive if you find a playstyle that suits you. But not addictive in a MMO style where you have to be on at certain times etc. Since you can save at any time you can play when it suits you.
Just walking around in the world is a wonderful experiance with its gorgeous enviroments. There are no classes so you get better at what you do. But you should decide early on if you wanna be mage or none mage user, cause you if you dont wanna be mage there is no point in spending levelups in mana for example. They made it possible for mages to be stealthy now so no matter what you pick you can do everything.
This is one reviews opinion:
"First off, if you have any long term commitments like say, a job or friends or a significant other, we suggest you ring them to make your excuses now - you don't want to get sacked or dumped over a video game, and letting your friends think you've died or been kidnapped due to lack of communication is just plain rude. Furthermore, it might be worth making sure that your gas and electricity bills have been paid, and that you have enough provisions to last you until spring. You're going to need time for Skyrim and lots of it."
So I say, if you wanna explore a whole continent, discover new things for a year onwards then yes this is a game for you. But as Tin said it can drag you in.