/endlurk
They're not that common, actually. Completed ones, anyway. Yes, there are a lot of game-based 'fics, but most of these don't surpass the ten chapter mark, because the author realizes how huge a task it is, assuming you're not rushing through it. Game-based 'fics, in my opinion, are ridiculously easy but ridiculously difficult as well.
It's easy in the sense that the plot is pretty simple: A trainer traveling ______ region, battling different trainers in hopes of reaching said region's pokemon league. Basing it off the games just makes things easier as you already have an outline prepared for you. All the basics are planned out for you, really, from the rival to the main character itself, assuming you're using the main protagonist from the game as your main character.
However, writing a game-based fic really is a daunting task because it is, in essence, still a journey 'fic. This requires writing not only about your character's major battles, but all the tedious stuff, like traveling from point a to point b. You still gotta to develop your character properly, not only as a trainer, but as a human in general. You gotta make it "interesting" and "different" enough to actually attract readers as no one is going to want to read a story that is just "game in 'fic form." This is your chance to put your own spin on things and to write how you personally interpreted events in the game. The character in the game are pretty much as flat as they can be, albeit showing a little bit emotion during a battle start/finish. It's up to you to actually breathe life into them.
With fanfiction, you need something original, something away from the games itself, which is why it's called fanfiction, because the fans make it and they make it how they want it to be; ideas away from the game/show/whatever. :(
Aren't most ideas usually somewhat based off an idea from the game/anime/manga anyway? o_O I know a lot of authors, while not basing their entire story off the game/anime, have picked out certain excerpts from the game or anime and twisted and contorted it into something original and interesting. And that's kind of what game fics are. The author "makes it how they want it to be" in a sense.
That being said, as long as you stay away from writing the game into actual text, the author would be making the story his own by putting his own twist on things. If you do choose to write a 'fic like this, I think you should be prepared to write something pretty ... massive.
