Bethesda Softworks - Community Q&A @ Edge Online

Why did you make Shivering Isles so big? Wasn't there a point where you were thinking about not making it an expansion pack and releasing it as a standalone game?
[From: Tim Chubb]

Pete Hines: No, no. I mean, Oblivion is such a big game, which sucks people in and has them play so much, that what makes most sense to us is to give those people something to do with those characters that they’ve attached so much to. So doing an expansion allows you to do that – it allows you to take those guys and go to a different place where you can do new quests and find new stuff, and at the same time go back to the original game. Because one of the things we find is when people play expansions, they play the expansion content but then they also want to go back and do more stuff in the game that they realised they never finished – like: “Hey, I didn’t realise I was that close to becoming head of the thieves guild – I’m going to go back and finish that,” and so on. So we like this idea of continuing this character that you’ve spent so much time addressing, and giving them more stuff to do without breaking it apart completely and just doing a standalone thing. That’s not something we do – we believe in doing a big game and then doing a big expansion.