I was considering whether or not to buy Dishonored, and watching gameplay of it on Youtube, when a thought popped into my head: is Dishonored free-roam? Can you go anywhere you want, similarly to Fallout or The Elder Scrolls?
Dishonored is mission based, with each mission taking place in a separate 'level'. That said, the levels themselves are very large, and within each one, you can essentially roam freely. The game makes much more use of vertical space than most other titles, and heavily rewards exploration and 'roaming' within each level. Furthermore, you can replay any mission at any time once you have completed it.
No, Dishonored is not open-world. The game consists of a number of missions which you progress through. Every mission is a small world in itself, which you can move freely inside.
The missions themselves can be completed in many different ways, which makes Dishonored non-linear but not open-world. There are also side quests available in the mission levels.