It is slow in the way that foreign movies are slow. You gotta understand that and enjoy the ride. This is a classic tale of not belonging, knowing something is wrong but not having all the pieces .... or any of the pieces of the puzzle. A life of trying to squeeze yourself into what is “normal”. Then in walks the answer and you start to make sense but not entirely in a happy way. That feeling of belonging to “kin” combined with the feeling of betrayal ... of being lied to about your beginnings. The wrenching decision regarding which world you truly belong in. Nature/nurture at its finest.
That same story can be told using race, genetics, social class, etc. In Hollywood, the puzzle is most commonly resolved by discovery of superpowers ... or secret royalty. This one just involves trolls.