Hey,
I've got FFI, II, IV, V, VII, VIII, IX and X and I have also played X-2 (borrowed from a friend) and got over half way through that.
I am not keen on the idea of spin-offs, I can't really comment all that much on whether I feel they work well or not but I like the fact that each game other than XII and a previous FF title (tactics if I am right) being set in the same world, ran as seperate games.
I have watched AC numerous times and although I was very impressed with the fighting scenes and overall graphics I felt the story lacked much depth. To be honest, I was actually more impressed with SW as a movie. I felt the story was better explained and most will say that AC didn't need a solid story because it had VII to fall back on but I feel that AC was a let down to it's origin. Like someone previous had posted, the idea about the orphans etc was weak in my opinion. It was just another way to bring Sephiroth back and I thought the ending with him was too rushed and expected.
I am looking forward to playing XII but I am more eagerly awaiting XIII, especially Versus XIII. It will be interesting to see a female as a lead character
If I can think of anymore I will post again