I like that the chapters are pretty much 'free play' in and of themselves, especially the first 4. If you want to be a completist you just have to do everything in a chapter before moving to the next one (well to really do everything you'd have to play multiple times due to the choices).Cutting you off from earlier chapters helps the story progress and lets them do things that couldn't be done in Oblivion. Every area that you pass through as the story progresses, the Outskirts, Murky Waters, and Vizima, all undergo drastic changes as the story unfolds especially as you wrap up the chapters. While you hang out in them doing quests the setting is relatively static (characters going about their days, the city not burning) but things tend to be in tatters after the story finishes up in an area. To go back to those places wouldn't make any sense.Like somebody else said, the reason games like Oblivion can let you roam free is because the area is mostly bland, undynamic. The villages looks the same and the people in the villages are going about their business regardless of whether you've finished the main story or not even started it. What changes in the entire Oblivion world as you progress? There's that huge statue at the end and that's about it.In summary, I think they've struck a fine balance between free play and linear story-telling. They let you roam free in an area, but then it can get burned to the ground as part of the story when you're done with it.