These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: The Chessgame Of The Gods
Broken Base: People who read the chessverse (or refuse to) either think it's an amazing and unique idea that gets pulled off well; a good idea that is poorly executed; or just outright awful. The fact that most of the stories rely heavily on blood and gore to paint Equis as somewhat of a Crapsack World may have a hand in this.
Griffin the Griffin and its sequel Falling Feathers get this in regards to the main character. Is he an Iron Woobie who becomes a badass, or just annoying and overpowered? The fact that he is almost undeniably the strongest (canon) chess piece only furthers this, but in the author's defense, Griffin the Griffin was only the second chessfic, so he's had tons of time to build it up.
From Nobody to Knightmare is either one of the best or one of the worst chess fics. Reasons for it being considered the worst include its moderately poor grammar and spelling and the frequent musical breaks.
To Err is Equine and its sequel To Forgive, Celestial have gotten both criticism and adoration for the various video game references caused by "articles" (and, early on in the former, the main character's video game-inspired powers).
Marty Stu: A few characters can be considered this for various reasons.
Weird Al Effect: Some people credit BlackWing, author of Griffin the Griffin, for creating the Chessverse. However, it was actually created by Rust, author of The Ballad of Echo the Diamond Dog, and BlackWing's story was just done on the same idea and eventually led to a crossover.
The Woobie / Jerkass Woobie: A lot of chess pieces are one or the other, based on their personality and exactly what they do in Equestria.
Iron Woobie: Either way, they're almost definitely this as well.