How is it possible that you played through in 10 hours? I've played 16 hours and I am on mission 6. Plus the figure doesn't take into account that the game plays so smoothly that I didn't spend hours fiddling and fussing and reloading.
It wasn't really all that difficult. There ARE only 9 missions, after all. Like I said, 1 or 2 deaths, no need to restart or reload, no need to explore everything. The levels are quite easy and the paths are blatantly obvious once you've played for more than a few minutes. If you invest in Possession "stealthing" through with 0 kills is easy as pie, too easy, even on hard. I *mostly* enjoy RPGs, but my diversions were 3D FPS from Wolfenstein up, including playing Doom and original Quake Deathmatch on dial-up servers, so "dying" in non-PvP is something rather abnormal for me in an adventure game. Without the deaths, without indecision, and without the desire to find every last valuable, it's quite easy to run it in 10 hours without rushing. My second play through took 8 hours, even though I explored and discovered more, on stealth. It's main goal, being an adventure game, it should have been at least twice as long, twice the content, without relying on the "action content" "difficulty" to extend play. That said, at least I finished Dishonored, twice, unlike the abomination that Dark Souls (mentioning difficulty as a method of extending play brought that to mind) was, which I quickly tired of.