The humor holds up well over many episodes because it is consistently sharp. Katarina grows both on purpose and by accident as she learns to survive in her environment, and the story goes in a logical way. The cast is enjoyable, and it's not just another typical group of bishounen either. The animation is flawless, and the start is memorable.
The decision to keep the main cast of My Abilities to just four characters rather than expanding the cast is understandable. Crimson Vow is the characters' group. Since the story was mostly about Crimson Vow, Millie and the other characters got the same amount of attention.
The partial lack of plot is what definitely affects the quality. In the first part of the anime, we simply get to know the main character and get hints that he will be strong. Apart from that, we don't get anything: no concrete plot with a goal and a point.