It’s a teen SF/fantasy type thriller with some horror and dystopian parallel world stuff.
If you liked things like the maze runner and similar then this may be just the thing for you.
For me it was entirely predictable, trope-ridden, and executed just like many teen and children’s movies. A long build up to an expected, action-packed anti-climax.
It leaves the door open for a sequel or TV series.
There are some good bits in it. Walter played by mcconaughey is suitably ruthless and evil. Though like many villains he needs to do some significant risk management. ‘Stop breathing’ in his calm (reverbed) voice is more chilling and effective than many bad guys’ ‘die!’
Elba does a fair job with a very limited character. The teen is OK if not sufficiently terrified at times.
Not great. Entertaining at times. Catch it on DVD or see it if you don’t have some cleaning to do.