Dishonored plays it safe. It's evident in everything from the Thief like mission structure to the levelling up between missions. A simple string of assassination jobs strung together don't make for a great game.
We need to get rid of the linear mission structure, the ping pong style of homebase-mission-homebase, to something thats more of an adventure. We need plenty of different locations and the gameplay should change frequently. The player doesn't always have to be in a hostile environment, the same location can be made to deliver a different kind of situation each time.
The same goes for the levelling. Rather than having strict control over when and where upgrades can be done, the game should open itself up a little bit, merchants and traders should be located within the levels itself so that players might visit them whenever the game allows it. I think it's always better to let players make more decisions, makes the game more about THEM.
Also, why can't I throw enemies off balance by chucking dead bodies at them?