I find their implementation to be lacking on all fronts. They suffer from the classic "OC character is more important than they should be" problem. Ideally, OC characters should be minor enough that they can be ignored, and should add flavor to the world. Stuff like fellow adventurers, shopkeepers, random villagers, etc. Not "an immortal being who's lived countless lives and has had a massive, but unknown, impact on the world."
Yeeeah, a lot of the writers (especially the contributors, but some of the mains, too) don't really get the core conceit of writing background characters.
Honestly I think TiTS does a better job curbing this tendency. You'll still catch someone's a-little-too-competent-and-special Mary Sue OC here and there, but for the most part the regular contributors seem to understand that background characters should have a degree of mundanity to them - or, if they must be a secret agent or brilliant engineer or something, they should be a functional type of character that gives the PC access to something.
Like the brilliant wandering doc (Bianca, I think?) might come off as someone's OC if not for the fact that her exact circumstances provide a way to have semi-regular access to healing while in danger zones. Her content isn't about how much better a Rusher she is than Steele.
When they do finish up with this game they really need to implement some stricter submission guidelines for their next title.