One characteristic could be its length. Since it was the first of its kind, it likely had a certain amount of length to fully develop its story. Also, it probably had some form of character development, even if it was rudimentary compared to modern novels. For example, if we consider 'The Tale of Genji', the main character Genji has a long journey through life, and we see his growth and changes.
In the first Sherlock novel 'A Study in Scarlet', it has a complex mystery. There are two intertwined plotlines.
Typically, the first noir novels had complex and morally ambiguous characters. They weren't simply good or bad. For example, in 'The Postman Always Rings Twice', the characters' actions are driven by lust and greed, blurring the lines between right and wrong.
If we consider 'The Picture of Dorian Gray' as a candidate for the first gay novel, one characteristic is the subtlety in portraying homoerotic relationships. It wasn't overt, as the society of Wilde's time didn't allow for blatant homosexuality in literature. So, it was more about the undercurrents of attraction between characters like Dorian and Lord Henry.
The first spy novels often had a focus on secrecy and subterfuge. For example, in 'The Spy' by James Fenimore Cooper, the main character had to hide his true identity and motives while gathering information.
If we consider 'The Sorrows of Young Werther' as the first. It has strong emotional content, mainly focusing on the hero's love and melancholy.
If we consider 'The Book of the City of Ladies' as one of the first feminist novels, one characteristic is its use of positive female role models. It features women from history and mythology who are strong, intelligent, and virtuous, countering the negative stereotypes of women at the time.
If we consider 'The Romance of the Rose', one characteristic is its length. It's a long, detailed work. It also uses a lot of allegory, with characters representing abstract concepts like Love or Reason.
One characteristic might be its use of the Spanish language in a more developed and narrative - driven way compared to previous forms of Spanish writing. It may also have incorporated elements of Spanish folklore or local traditions.
Well, 'A Contract with God' by Will Eisner is often considered one of the first graphic novels. It had a more complex and serious story compared to typical comics at the time, which makes it a strong candidate for being among the first of its kind.
One possible characteristic could be a strong sense of tension and suspense. Since it's about a hostage situation, the author would likely build up the feeling of danger and uncertainty. Another might be a focus on the relationships between the hostages and their captors, like how they interact, negotiate, or struggle against each other.