Family Drama, Mystery, Young Adult Literature
I'll Give You the Sun is, first and foremost, a family drama. Jude and Noah, the protagonists, are twins, and their relationship is central to the novel (even though they're barely speaking to one another for most of it). In addition to that conflict, they're each trying to deal with the fallout from the unexpected death of their mother. That's right—these two are dealing with a lot of drama about their mama.
Thanks folks, we're here all week.
The novel's unusual structure—it alternates narrators, with Noah reporting out from age 13-14 and Jude's narration picking up two years later—make it so that we readers have to piece together the story to some degree. Though it's a far cry from a hard-boiled mystery novel, the plot is driven by little revelations that help us "crack the case" of what went down between brother and sister.
Along the way, we watch Noah and Jude grow into their authentic selves. Given that personal progress and the characters' ages, it's safe to assume we're in the land of Young Adult novels.