Actually Stealth and Popularity are crucial factors in Assassin's Creed. With the former you can approach your target undected until it's too late obviously, and with the latter if you earn the respect of the local populace they will passively or actively help you especially during escape after you kill your target.
Assassin's Creed is the new game created by the POP Team, that made the new Prince of Persia trilogy. You can have several informations on it on the official site !