It's a luck game.
It's a neat concept, really... but there's no pattern. It isn't about skill.
It's about hoping that the random-walking-around AI decides to make the target wander in a clear spot, hoping you can hit it, and then hide till the hole appears.
Why can't I study my target's pattern to learn that he goes to a certain spot, relatively alone, every 30 (game) seconds? Or how about the guard patterns? Why don't they have regular patrols.
You have to be lucky for the AI seed to make them wander in a position that works for you, and hope they stay in that lucky position long enough for the mission to end. An assassin is one who knows where his target will be and how to get there before anyone sees it.
Too much luck, really brings it down. Neat concept, bad execution.