The first Assassins Creed is fun in the sense that you wouldn't expect its potential, between the gameplay which is ok but repetitive, the story which is good but seems written by an edgy teenager or an old man trying to apply cool plots to each other on paper (or both, I don't know how Ubisoft Montreal works), and the visuals with the X360's first half generation gameplay bifuming.
I like it for the wrong reasons or it's great, I don't know, but it's the first of a trilogy (or pentalogy depending on how you count it), and it's important to its plot.