Luis_989’s review published on Letterboxd:
Mother poses an enigma, both for the narrative and for the viewer, and the enigma isn't that complicated; A young man with an intellectual disability is charged with murder.
The clues point to him, and there are reasons to believe it, but there are also reasons not to do it, and these fall on the mother, totally willing to try and show it.
So the deal is to find out if he did it or if he didn't
Fortunately the film doesn't provide easy answers, and this is appreciated because it doesn't try to complicate the plot more than it should.
It's evident that there is a good argumentative construction, and Bong Joon-ho knows how to sustain the tension without overstretching the viewer's patience.
Mother is not what it appears to be, and it's deceptive enough without trying to anticipate your own guesswork, and that's an incredibly difficult thing to do. Especially when it comes to thrillers.
But this isn't your conventional affair, and for that I thank the director.