Over the years I have read a lot of books. I mean, a lot of books. Now that I sit back and take a look at them, there are a lot of similarities between all of them.
Some seem just like others with the exception of the characters names and location and there is nothing wrong with that, as although the books are similar, they are still great stories.
However, I have learned that the more original your manuscript is, the more likely it is to be published. I am not saying that just because your manuscript is bold or pushes the envelope that it is going to be published.
Your writing style is a big determining factor there, along with editing. I have seen publishers send a rejection without bothering with looking at the manuscript because the editing in the query letter was poor.
Take your time and be original. Don’t piggyback off of someone else’s idea because you think you can do it better or because you are in a hurry to get your name out there. Be yourself. Write what you like and don’t worry what is “in” or “popular” at the moment. You never know, what is popular at the time may fade and what you are writing could come in demand.