Voted 'other'.
I like that I don't
have to do the main quest - or rather, that I don't have to do it except when I want to. But I don't like games that are pure sandbox either. I like a sense of progression, of increasing challenges that have to be overcome. And while I like the freedom of the Elder Scrolls games, I also like the structure that a well written story gives.
If there's no main quest, no story driving things along, if quests can be done in just about any order you like, then for me there's no sense of achievement. It's just a diary with a list of 'things to do' that can be done as and when.
Of course, I appreciate that's great fun for a lot of people, and sometimes it's great fun for me as well. It just isn't quite
enough fun
.