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.
Older than You Think: Most people would assume that Jokers appearance in this story is inspired by the Heath Ledger Joker in The Dark Knight, but this Joker was actually designed long before the first images of Ledger in makeup went public. The similarities are a complete coincidence.
One-Scene Wonder: The Riddler shows up in a single scene and comes off as the most competent and awesome criminal in the book.
Batman also only appears in about four pages, and aside from the word "Us?" he has exactly one line. And it is awesome.
Squick: A lot of the scenes involving the Joker, in particular some of his more gruesome murders, but a genuinely creepy example is of him doing something as seemingly innocuous as eating shrimp in a thoroughly revolting manner.