I know this would be really hard and take up a lot of time, but you should be able to be a true assassin and have disguises and kill the guards, but once alarm is up, it shouldn't go down. Just to make it a bit more realistic.
@TheMysteryOfPi: The whole point of invisibility is to use it when you are hiding around a corner and they walk around before you can move. I personally found invisibility to be very useful, I even used it in the middle of a hallway and a guard walked right past me. To be an ultimate assassin you use your tools as well as your skill.
Put a + If you agree that the next doodle god, not only should you see the population, but if you have to many vampires and stuff, you have to make more humans and other things.