I could list the many problems with this book, but four hundred words limit me so I will stick to one point.
The main issue with Avengers Arena is that it is the sequel for four series yet it constantly ignores continuity in not just the artifacts and abilities of characters, but also their personalities. Avengers Arena would be "well-written" if you ignored the ten years of the Runaways and Sentinel, 3 years of Academy, and god knows how many years of Darkhawk. Because these blatant ignorance of the character of these series, Avengers Arena becomes plot driven instead of character driven. In which, the characters are being affected by the plot when they shouldn't be. 3 points of analysis.
If this were a character driven story, X-23 would not have rushed out in the open against Apex. It has been established since the character's inception that she was trained to kill at maximum efficiency. Even in Arena, they established that she immediately thinks of ways to kill people the moment she sees them. She would have saw the threat and think of the better way to off Apex.
If this were a character driven story, Apex would have killed X-23 or at least tried harder.
3. Nico Minoru
This is were it gets blatant. Nico is in possession of one of the most powerful magical artifacts in Marvel. It has been said that the Gods of Marvel rather not deal with the wielder of the Staff of One. That said, this story expects me to believe that Arcade and his minion somehow managed to do something that omniscient beings with working knowledge of the Staff couldn't do? But that is not the character part that bothers me since the Staff of One is not a character(per say). Nico would not let this situation best her. This is a girl who was creative with her spells for ten years prior to this debacle and would be too intelligent to not signal for help. She was resourceful to the extent that if one of her friends betrayed her again, she would have spell specifically tailor made for the scenario. She is too smart and too powerful to let this situation best her and because the sake of the plot, she has been killed(or resurrected) just to make the story more grim.
Again, I could go on about the many flaws of this series, but I will cab it here.