A good question. Let's examine what you've told us, and see if we can find an answer.

Pros
Good writing style
Good SPaG
Easy to Read

Cons
OOCness

Neutral
Author is fun and quirky
Fic is an AU

Looks to me like the Pros far outweigh the Cons. I can't say for sure that it is badfic but, even if it is, it is probably not bad enough to spork. We aren't looking for fics that are just a little bad, after all.

As a side note, I put AU under Neutral because I sometimes hear people use it as a negative when talking about a fic, but there is nothing inherently wrong with an AU. It is a genre. Genres are neither good or bad. They simply are.

-Phobos

Another big part of the sporking selection process is effort. Many of the fics that get PPC'd clearly have no effort whatsoever put into them, in terms of SPaG and closeness to canon. In your opinion, did the author put a lot of effort into the fic?

Also, Popularity =/= Quality. I've seen loads of lazy, badly written, or disturbing fanfics that don't have a single negative review.

Thirdly, and most importantly, would it be funny? That's probably the main deciding factor. Would it be funny to spork it? Could you get a lot of jokes out of it, or at the very least a lot of development for your own characters?

Is the fic enjoyable to read?

Badfic is badfic because it isn't written well. (Yeah, a Captain Obvious). If the story all in itself is good, then it isn't a badfic.

Take Shadow Cristal Mage's "Nanoha Takamachi of 2814". OOCness is rampant, but the story is really well written. Yeah, it's a crackfic, but it has also an overarching plot. A truly masterpiece.

The two major warning bells of a badfic are bad grammar and flimsy plot. (For example, the one I posted just under this has a few holes in the plot, and a not-so-stellar grammar), and by your review that's not the case.