Seriously? Twelve?
I won't fall into the trap of saying, "well if you thought that was good, you're WRONG", but in terms of storyline and very specifically soundtrack, character and plot development (that didn't invovle buying the numerous spin offs), there's a lot better games out there.
Twelve did exactly what it said on the tin, it was a graphically great game by PS2 standards, a huge game with an expansive storyline and unique customisation abilities, but somewhere along the way, it lost the humour and personality of some of its perdecessors, or so I thought anyway. I didn't find the characters all that likeable, and at times they just seemed a little irrelevant. It tried too hard, and didnt have enough back story for me.
Personally, I liked ten, but six is a very close second. Very close.