What can I say? Ubisoft Montreal made the word "Assassin" popular. This game lasts more than 20 hours of gameplay, and really is fun; well only if you play less than 3 hours a day, since it can become repetitive, but if you avoid that, you won't get tired of this game.
It's best if you play this, before continuing onto the recent release of Assassin's Creed II, since you won't know the storyline AT ALL, and after playing the second one and then playing the first one, you will think this isn't as great, so play this first.
Graphics are stunning, and a must to play in HD, since you really are missing out playing in SD. Most of the people who say it becomes repetitive play more than 3 hours a session, which is sadistic and also unhealthy, so don't get discouraged by the large amount of people saying this isn't as good as it sounds.
Must have for a Xbox. Assassin's Creed II as well.