Being influenced by something is fine but it doesn't have to be a carbon copy of the film. I personally liked contrasting the intro of the hero with the intro of the villain. The scene doesn't show much of him but enough to be intrigued. And there's two points to consider...
- If we don't see him and only his killing, mirroring the movie Seven, it would mean that he is already the criminal mastermind we know from the comics, which he isn't. Just like we're witnessing Batman's beginning (two years on the job is not much), we're also seeing the beginning of The Riddler and if he returns in future films, he will hopefully be smarter and learned from his mistakes.
- We only knew it was the Riddler because of all the marketing and trailers. If you would've gone into the movie without having seen anything of it beforehand, would you have guessed that this was supposed to be The Riddler?
Also that scene is important for a specific aspect of my edit, which I'm not revealing at this point...