Finished DotO yesterday. It took me 14 hours, apprently, which is pretty good value.
A bit shallower (but perhaps a bit leaner in some respects) than the previous games, I thought, and the last levels were much too linear to do justice to the franchise. Whilst I like Billie Lurk as a character from D2, I found her disappointingly one-note in this outing, and the story felt a bit stretched out depite the relatively short playtime compared to the other Dishonored games.
Still, I love Dunwall and Karnaca as settings, and most of the level design (up to mission four anyway) was as accomplished as you'd expect from this series. Feel a bit sad that I'll not get to explore these settings in a game again, and I'd love to see Arkane find a way to make the settings work for future games. Or maybe they'd be right to leave us all wanting more, I dunno.