Bad Superman
What if superman was a bad guy? That's the premise Brightburn is built upon. 
To my mind its a more mature concept than the traditional good guy Superman. It makes sense on a certain level too. A superior being would inevitably assert its superiority over lesser beings. That's how evolution and predator/prey relationships tend to work.
Whether you agree with my Darwinian assumptions or not, this is a decent horror sci fi film. There's a sense of the comfortable and familiar family dynamic being turned on its head. The innocent, much loved, adopted son, transformed into something so overwhelming powerful and ruthlessly destructive, that even his parents come to fear him. 
Its the abrupt contrast between these two realities, that makes this film genuinely unnerving.Helped in no small part by a clever climax, that underlines the fall from grace humanity faces, at the hands of this alien other. 
A decent watch I rate 7/10.