Not every character is the same. Not every story is told the same way. There are books that seem light but have darker undercurrents. Books that uplift you, that are quirky and completely their own thing. Which is why it's so important to find the perfect tone for your story. Sometimes it can take a while to hit that perfect stride, but I promise, if you keep at it, you'll find just the right way to tell your story. The authors I admire most are great at conveying the mood of their book through various methods, the way a character speaks, the setting, the prose.
Take the Hex Hall series by Rachel Hawkins for example. It's a fun read, Sophie is a character full of hilarious inner dialogue and witty comebacks dealing with some seriously messed up stuff. If you look at the story just as 'fun', you'll miss the deeper issues taking place, such as the abandonment Sophie feels because of her father, not being able to trust the guy she loves, the secret her mother keeps from her, anger, fear- all those things are there. The setting is a perfect background for all the crazy that unfolds, but it doesn't overwhelm the reader or the story. Sophie never loses the thing that makes her her while she's at Hex Hall, because it's her voice that makes the story.
Then there's The Scorpio Races by Maggie Stievfater, a book where the setting sets up the mood in a major way. It's a freaking island where angry, murderous horses wash up and try to eat you for crying out loud. It's the perfect place to establish the tone of the book. You know right away that this place is dark, that dreams die beside the harsh reality of the island's life. In this story it's not necessarily Puck or Sean showing us the bleakness of the island's history or the fear of what's ahead in the race, it's the island itself that carries the story, that molds how the story is told. Sean and Puck are just a way for us to be introduced to the island, the eyes that help us to experience Thisby.
It's important for the author to establish the tone and voice of the story within the first few sentences. It's also important that it continues throughout the book, consistency is key. And it can be hard to get the hang of it at times, but once you get into the groove of things, the story really takes off. It's also important to be honest and genuine with the story, don't force it to be something it's not meant to be. A lot of times a book will feel flat or fizzle because there's too much going on, the reader doesn't connect because they feel overwhelmed. Like I said, it can take time to figure out the perfect way to tell the story, but the end result is worth the trial and error. And the reader will thank you for taking your time to tell a story only you could have in the most authentic way possible. No forcing or pushing involved.