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.
Complete Monster: Former Number 1, Roxanne. With good looks to fool you, she's regardless an absolute sadist, especially in regard to her former comrade Cassandra. Her Moral Event Horizon, as revealed in 119, is causing the death of Cassandra's only friend, then mocking her to make her go berserk on the other Warriors. She then impales Cassandra's head with the sharp pommel of her sword. The Awakened Being killed Cassandra's friend very, very slowly, and it's implied it raped her. Roxanne cheerily says she looked like she was enjoying herself, so interfering wouldn't be right.
Glurge: Through all of the hardships that Clare went through upon becoming a claymore, considered to be a failure and ridiculed because of so, she was able to press on because she always had Teresa with her... Very literally so since Clare was able to become a claymore by having the flesh from Teresa's decapitated head implanted in her.
God-Mode Sue: Priscilla. She's so incredibly powerful that no one can beat her, that even a piece of her arm is enough to possess Abyssal level Awakened Beings, and she hasn't lost a. Single. Battle. Gets quite annoying how the goal Clare had set for herself is unattainable with these odds.
Lets make it clear: she's making Madara fucking Uchiha have a harder time against opponents than Priscilla does. Priscilla even survives being cut up into tiny chunks! To clarify: while pretty much all of the characters have been sliced and diced in some way at one point or another, Priscilla's head is also sliced into tiny chunks. And somehow she manages to get to Cassandra's corpse, at least a good hundred feet or more away, and start chowing down. Despite having been in bite-sized pieces.What.
Perhaps an Ass Pull won't be needed after all, as Teresa coming back was hinted at earlier in the story — her presence inside of Clare was implied even as far back as Clare's first meeting with Miria, when Miria told Clare that Clare's rank bothered her because it had felt as if "the strongest was standing before [her]". Turns out that in a sense, it was true.
Roxanne's habit of Mega Manning the signature techniques of more powerful Claymores then killing her teachers was born of a twisted internal logic that makes putting her down pretty much mandatory, but watching an Awakened Being rape and torture a far weaker Claymore to death without lifting a finger to help moved her from the "Cut her head off now please." category to the "Will someone invent the wood chipper so she can be fed to it feet first?" category in the eyes of many readers.
Too Cool to Live: Teresa, Jean, Flora, possibly Ilena. Miria would have counted had she not been spared by the other Claymores. The author admitted that if Teresa had survived or were somehow revived, he would have to rewrite the whole story.
On the villain side, the original Abyssal Ones, and Chronos and Octavia, as of chapter 149. Yes, they would have had to die eventually but still...
Villain Sue: After many contenders, the true Villain Sue can only be, without a doubt, Priscilla.
The Woobie: By this point, it is easier to count the characters who are not Woobies on hand. The men of the organization, bandits, Roxanne, and most male Awakened. Everyone else needs a hug, a glass of milk and a plate of cookies.
Cassandra, a Shrinking Violet who has, by chance, discovered a technique that she loathed but which propelled her to #1 of her generation. The only person who didn't loathe or fear her, the nameless #35, was killed in a disgusting, brutal, and completely senseless manner due to a Manipulative Bitch's machinations. Then, she was summarily executed by fellow Claymores. And on top of that, she was resurrected, brainwashed, sicked on her fellow warriors, and eventually awakened, tricked to fight Priscilla—only to be devoured by her just as the Ghosts seemed to have offed her for good.
Woobie Species: All the Claymores were orphans who were unwillingly put through painful and life threatening surgery so that they could fight man-eating monsters. Even the strongest ones don't get to live very long.