Well, to me, Final Fantasy XIII was the spin-off, in comparison to Versus, in my eyes, Versus is the REAL '13' FF iteration, not the SPIN-OFF.
To me FFXIII feels like the Greatest Hits album which came out when I expected a new hit album with NEW SONGS from my favourite artist, metaphorically speaking, SQUARE ENIX.
Does anyone understand what I mean by this??!!
I expected original FF Content, and received a character which emulated Cloud, a man which reminded me of Barret (trying to convince me to fight, whilst also having a child), a 'Hero' Snow who was a mash of Seifer and Zell. The sister, which 'died' (OMG Aeris-Ancient)
To me, the success in character design was only Fang. She was the breath of fresh air I looked for. I expected originality in this iteration, at least sevenfold with a fruitful cast.
To avoid annoying anyone here, I just wanna say that I am disappointed as a fan of Final Fantasy. XIII is going to make me suffer more with it's 2nd iteration, a kid who looks like he was a copied asset from Kingdom Hearts, and a Chocobo Race mini-game and a 'Golden Saucer' to boot. I want to enjoy it, but I don't want to feel like I am playing a game made lacking originality in design, risks taken with fresh efforts, and a boldness to reward your audience which has played your series through the years. You want to please new non-FF gamers, don't dumb it down, and if so, make it optional.
Wanna implement a materia-similar system again??? RE-INVENT IT!!! Look at how Skyrim does enchantments, Look at how Xenoblade allows for similar weapons modification, they are utilising the charm of a materia system without simply and blatantly copying and renaming it. (Yes, I am aware they are all from different developers)
I don't want to revisit the Golden Saucer with "Roxasora", unless it is FFVII related. You want new ideas, create a sequel which exists in space, where people believe in a second crystallic "earth", and find it. have a town which exists inside a large tree. [Just wrote a badass synopsis I would have loved to be a Final Fantasy and decided to hold back and work on it. So far it beats FFXIII's story by Aeons

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I have to send Square Enix a letter, I have too much to say regarding Final Fantasy.