Opening Statement- The Fictional Story of Assassin's Creed is great and addicting.
Brotherhood continues the story of Ezio Auditore De Firenze and his role in the revolution of Roma during the early 1500's. Brotherhood also leaves Desmond in a massive cliff-hanger but I'll get into that later.
Story
Brotherhood has a great storyline that still has Rodrigo Borgia as the Main villain but another baddie, "Cesare", is your #1 target throughout the game. Many many guards and important people fall under your blade and the fiction/non-fiction flip-flop is great to kill the boredom you might feel running around 16th century Rome.
Ezio can now recruit assassins. Your assassin's can aid you in missions, attacks, and mini missions where they can level up and get new equipment.