The first 45 minutes is great, and it was really thrilling. The second mountaineering sequence had my mouth hanging open and loudly saying "holy shit!"
However, the last act and maybe the second half of the second act is where things turn sloppy. Plot holes, irritating directorial tics (calm down with the slow motion, man! Who are you, Zack Snyder?), and a complete change of setting make the second half of the film completely uninteresting and I couldn't wait for it to end.
It's a shame, had the film kept up with the mountaineering setting and the well put together set pieces it could have been something special, but instead it's just wasted potential.