Dejan Stojanovic said in his book The Sun Watches the Sun “The deeper thought is, the taller it becomes.” Stop and look at that for a moment. Basically, what it means is "the deeper the thought, the more visible it will be". I've been doing a lot of book reviews recently, and I've come to realize one simple truth: it's not necessarily the quality of the writing that makes a book great, but it's the depth of the story. The books I've disliked the most are the ones that have no depth to them. They're all story and very little character growth, challenge, or change. It's all about telling a great story, but without actually getting you to relate to the character. Then, there are the stories that are considered "classics"--The Grapes of Wrath, The Great Gatsby, 1984, Animal Farm, and so on. These stories have a lot more depth to them. They look at serious issues--with society, politics, religion, or humanity. They may not be "light" reading, but they are the books that "stand tall". Not every book can get into a discussion of socio-economics and its effects on the religiosity of blah, blah, blah, boring, dull humdrum. You're writing fantasy, sci-fi, mystery, or thrillers, so do you really need to get into deeper issues? I wouldn't discount the idea! Your main character may not be a philosopher, but he/she can still ask some questions that force them (and your readers) to think about deeper issues. The best books, I have found, are the ones that get people thinking and talking. Everyone loves to talk about how controversial Game of Thrones is, but that's what has made it one of the most popular novel series/TV shows in recent years. People are talking and thinking, and it doesn't matter how long and hard the books are to read. They've grabbed people's attention by offering a simple premise: what are you willing to do to achieve your end goals? Find that "something deeper" in your story. It doesn't matter what genre you are writing--add depth to it! It is the deepest stories that will stand the tallest.