I'll cut to the chase: the movie wasn't good. It was entirely too short, precious little was done to provide any empathy for the child. He seemed creepy pretty much from the hot second you see him until he begins a homicidal rampage. A few shining moments come through where he gets along with his parents...but they don't do enough.
The film needed to show him interact with other people in positive ways but have the negative elements of his environment overwhelm him. Or, take away the bullying aspect altogether and allow what amounts to the 'real' catalyst to push him toward being a sicko.
Probably the greatest crime the film commits is in misusing the cool child actor who did a fantastic job in his role. He deserved more time to develop that character, to show more of anything at all. Instead of tragedy, you get exactly what the trailer prescribed: murder and a predictable path toward a potential sequel.
I liked the three leads in the film. Many of the other people didn't show up nearly enough. Some of them straight phoned it in. Everyone did a good job when they were scared though, and since that's the majority of the film, I guess I can't fault the acting much.
Let's briefly discuss the gore factor: holy crap. I haven't watched many horror movies recently that rely on nasty to get a reaction. There were a good five people in the theater who made some noise when stuff happened in this. It was bad. I'm not sure it's like...warn you not to see it bad but it's definitely look away if you're sensitive bad.
One thing I really liked was the discussion held in the film between the parents about what they'd done. When they put it in context, that they found a 'thing' in the woods that happened to look like them, it does make Clark Kent's parents particularly lucky.
Final thoughts: Brightburn was a moderately interesting idea that everyone already thought about but someone finally made it into a movie. Unfortunately, it wasn't good and I don't really see any reason to recommend it to anyone unless you can see it for free.
Even then, if you've got another option, Brightburn should take a back seat.
Rating: 1 out of 5.