(Note: I am only about 1/8th of the way into Kushiel, a 700-page book.) (Side note: all my discussions of YA books are geared toward adult readers. I will not look at books from a youth's perspective, nor will I venture to make recommendations or identify readalikes for teens.)
I went into The Giver knowing nothing about it, save that it was a classic, a good book for boys (an impression I garnered at age 9 when it was published and read by my brother), and that iconic, mysterious cover image with the bearded old man. All the background I had on Kushiel's Dart was that it was series fantasy with a female protagonist, and there were BDSM themes (the final notion came as a caveat from a friend recommending it--I was undeterred).
Both books create worlds and detail with a child's nonchalance (naiveté?) the rules, norms, and "politics" of their settings. The main characters of both books, in the beginnings, narrate their coming-of-age (Kushiel in first person, Giver, third person limited) as they wonder about, anticipate, and come to understand through describing to the reader the regulated changes happening in their lives as preteens.
I wouldn't necessarily recommend either book to a fan of the other, but their trajectories are so far quite similar. Kushiel is way more detailed and complex, the language more sophisticated. But, for being adult fantasy vs. YA fiction (surprisingly not characterized as sci fi), the two may be sisters, just of very different maturities.