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: Arkham Asylum: A Serious House on Serious Earth
Harsher in Hindsight: The Joker's crack about Robin was written before Jason Todd had died in the regular books but the book came after. Morrison noted all it did was add another layer to the Joker's audacity in saying it.
One-Scene Wonder: Maxie Zeus only appears for one scene, but leaves a major impact. His only real role is to talk to Batman a little bit and not get any response, but his speech is chilling and sets the mood of the story perfectly.
Sequelitis: A "spiritual sequel", written and illustrated by SamKieth and entitled Arkham Asylum: Madness, was released in 2006.