Language has a lot to do with voice. What is it about your characters (in whatever world they are in --this world, a Dystopian world, another world, etc), and how they talk that make them unique?
What do I mean? Look at Maze Runner, a fantastic example. These boys are in a maze with no memories, so they start making up their own names for things and using their own terms in place of "stupid," "lame," and the F-bomb. They have developed their own language, but one any reader can easily understand and believe.
Across the Universe also achieves the same, though not to quite the extent. They say "brilly" instead of "brilliant" and "frex" in place of many swears.
And, though I hated the book (respected yes, but it's one of those things that creep the heck out of me, like Chuck Palahniuk or Thomas Pynchon), Feed by MT Anderson also has great language. So much so that if I read too many chapters at once, my internal thoughts starting sounding like the narrator. Talk about effective.
Once again, all my examples are dystopian or futuristic or sci-fy. On the contemporary side, John Green is a master with language. Specifically, An Abundance of Katherines, in which their F-bomb substitute has a nerdy explanation. Not only is the language amazing, but it plays directly into VOICE.
I'm not expecting you to go so far as to create an entire new language. But (they'll be speaking English I hope, haha) they need their own way of speaking. If your story centers around a royal family, how is their speech different than a commoner's? If they are on a spaceship, I hope that their language (and VOICE) reflect a scientific bent. If they believe in multiple Goddesses, I don't want to see "Thank God"--use maybe "Thank the Goddesses." If it's a contemporary novel, how does the character's use of language reflect their voice?
Language/voice isn't only about replacing a few F-bombs for censorship-sake however (please don't do it for censorship-sake, do it because it fits your world and characters--if your world and characters drop the F-bomb every other word, then have at it!). It's about creating a language that's engaging but realistic, something that makes your characters/setting engaging.
So, based on language, what are your favorite novels?