Andrew Buckle’s review published on Letterboxd :
This is as unnerving, brutally intense and realistic as any prison drama I have seen. The performances are terrific - so convincing, especially from young Jack O'Connell, that if I were to ever see these actors on the street my first instinct would be to run the other way.
I liked how focused the film was - we never leave the prison and though we are introduced to other inmates it is solely about Eric Love's experiences - aligning us with an extremely volatile and violent prisoner who seems incapable of reform and thrives on disruption and chaos. Rehabilitation seems impossible, but the organic way we see him change through his unexpected bond with others in a support group environment is very well executed.
There is a tension throughout the film between the influence of the penitentiary facilities, and the corrupt methods initiated to control Eric, and Eric's own imprisoned father (Ben Mendelsohn). Neville has has never been there for his son when he needed to be, but his attempts to prepare his son for survival in this prison, and his guidance on how to behave, falls on deaf ears. Eric makes it clear he can't be controlled or suppressed by powerful individuals, and his relationship with his father worsens when circumstances reveal themselves, which ultimately places both of them under threat.
A bone-crunching, horrifically realistic document of prison life, it is extremely affecting in places. You feel trapped inside the prison and no matter how strongly you feel about trying to escape, it is too riveting.