It took me a week to finish the (quite short in comparision to the other assassin's creed games) storyline, now going to finish all the side missions and such. In order to understand the story, i do recommend you to play Assassins creed 2 before starting brotherhood. Assassin's Creed 1 should also be played, but i didn't play the game beceause i didn't understand a shit of what they said (no subtitles). However, that was 2 years ago, i should try playing it again.. Maybe some questions get more clear. 
Ahh okay - AC: Brotherhood's the only one I have, but quite evidently is part of a series.
I will have to check the others out one day, perhaps.
Thanks for the info - it's got to be one of my favourite games on the PS3.