As one reviewer said, this is an existential puzzle box of a movie, the true meaning of the title being revealed at the very end. It's not just about escaping from a prison, nor is it a pretentious metaphor. Its just very very well made.
I appreciate some similarities with Shawshank Redemption for obvious reasons, but really this film stands up on its own rights. The reasons for escaping are wholly different - SR was to right a wrong while here it is familial breakdown and taking responsibility for ones own actions. Brian Cox's character, and the rest, are believable and fleshed out enough to engage with but the real achievement here is in the pacing and structuring of the plot.
The film cuts between the actual escape itself and the events and planning leading up to the escape. Dominoes, diamonds, and of course, drugs all play a part in the set-up of the escape, which plays out with breathless excitement. The grim presentation of the prison, Damien Lewis' character in particular, appears shockingly believable. Prisons are not ruled in the way they should be, and a character like his, having a grip over the institution rather than the other way round, seems sadly truthful. He is very scary...
The end, like Shawshank, is uplifting in a downbeat kinda way. It reminded me of The Descent, which i hope is not a great spoiler for people. I almost cried but actually you're left feeling quite happy for the central character. There is not the same redemption as SR, which is a good thing, so don't go in expecting happy endings, or heaven forbid, Prison Break The Movie. For that it is not, though its existence probably owes something to the success of that over-running TV show, and the ingenious escape route is one Michael Schofield would be proud of. But really, this is a great little indie movie which came and went at the cinema very quickly, but will no doubt find an audience in the years to come.