I believe the best way to sum up the issue is whether the changes to the Canon are Plausible. Is it within reason that such a change could happen.

So, if drastic changes happen to say Harry Potter during his time at Hogwarts, then it is a high risk of being a bad story. However, if say subtle changes that occur well before the books happen, leading to more drastic alterations later one, that is probably more acceptable.

Everyone has a slightly different view on this, but most people find lack of plot, bad grammar, spelling and a Mary Sue in the fic in question to greatly detract from it's goodness.

I would like to add, though, that in general I find that the amount of likes a story has is irrelevant in terms of badfic: I've PPC'd badfic with no likes and I've PPC'd badfic that was liked by people.

As for the changes issue you brought up in the second paragraph... our stance is that changes are not really an inherently bad thing. However, with some changes to the canon you can go too far, and that's where we come in. It's sort of like what the Nostalgia Critic said about The Last Airbender: you do have to make some changes, but they've gotta be changes that make sense. I don't know about your two Dragon Age fics (I'll give 'em a look later if I have time), but given the quality of the writing style I don't think there'll be too much to write about there.

And since you're here... welcome to the PPC, dude! Have some music by Bruno Maderna as a welcome gift: http://www.youtube.com/watch?v=faSImo7Aa3A

We each have our own idea of what's good, bad, or mediocre, but I think what's most important in our badfic selection process is if the badfic itself is funny ("funny" being anything that falls in between "mess of funny typos" to "completely inane plot"). We write missions to make our agents cry, rage, and go nuts over silly happenings, so we choose materials that would enable us to write a good scenario for them. Think of it as a MST shot on location, except the audience gets a chance to fix things at the end.

As for FFN (and other sites that host fanfic) reviews and "likes", I find them to be a general indicator of what's trending as opposed to what is good. Consider the slightly horrifying appeal of the Fifty Shades series... It's popular, but a lot of us wouldn't say it's a great piece of literature.

Oh, and hello to you, good sir/ma'am/mysterious entity! We hope you enjoy your stay on the Board.

Here's a link to The Last of Us post-ending story on The Pit I found recently (http://www.fanfiction.net/s/9402093/1/Their-story). It doesn't seem bad by the looks of it and has 137 favs. at 36 k words. Does this actually mean anything in terms of the story quality or not? I don't know if you have done anything in the TLOU universe yet, but I hope you'll find this message useful.

Then, here's another story on the Pit (also available at the Dragon Age wiki) I'm not sure about: http://www.fanfiction.net/s/6852833/1/His-Father-s-Son and its prequel of sorts, http://www.fanfiction.net/s/6488069/1/Necessary-Things (plus some oneshots related to both stories.) I have been reading this for quite a while and I can't quite make up my mind on it: it is close to canon overall, but some later chapters do begin to change things and I'm not sure about the characters' handling. Essentially, my opinion of it changes from chapter to chapter and I was curious as to what you thought of it and how it matches with your quality requirements.