Assassin's Creed seemed to have a problem with taking all it's great concepts and flawing them.
Large Responsive Crowds - Sheepish AI and ineffectualism
Free Running - Matrix-style jump system that would you send you flying backwards off a wall, probably into a mob of Crusaders who you were trying to escape from
Medieval and Futuristic Storyline - Long, boring, unskippable cut-scenes
Being an Assassin - Lack of ability to plan Assassinations, couple with the complete omission fo stealth
Free Roaming - Linearity
Oh, and whose idea was it to include the lepers? It's not that I don't love them hitting me, or blocking the way when I'm trying to assassinate someone.