Tried it. I used to love writing short stories but only short ones, I found that the longer it went, the more boring and uninterested I became in writing it. The longest original piece I've ever written is about 20K words.

Yeah, as I was saying. I tried doing an FFX: The Novel but as I've already explained, it grew tiresome for me really quickly and after I got up to Djose Temple I had to delete the awful thing. Surprisingly, without being surprising I discovered that I had been kinda inventing my own little side stories along the way. Example: I had given the characters surnames, given several NPCs a few moments in the spotlight and replaced Maechen with reoccuring dreams that Tidus had every now and then because I thought it be more symbolic of his connection to Spira and Sin.

I realised that I prefered writing original stuff because I could let my mind just kinda flow and come up with whatever without being bound to the restrictions that would come with writing a fanfic or in this case, a novel version of a game.

But everyone's different. Personally, I wouldn't try it again but I am looking forward to seeing how well you can make your's out to be.