One of the biggest flaws of this movie, as many others stated before me, is the bad writing. I won't go into details but this movie will make you wonder if the characters on screen have any brains at all.
Yes, the director is at his first directing role but still, that doesn't give you permission to write a weak scenario.
Basically the whole action is similar to Assault on precinct 13 or Home Alone for that matter: some bad guys trying to get inside a house and they have a hard time achieving that goal.
The acting is weak as well but decent at times. Jason Momoa fails to deliver a role that was designed to be badass but clearly is not, although he has the weight of the whole movie bearing on his shoulders. Stephen Lang isn't something spectacular as well. As for the rest of the cast, well, it felt like they were rookies at this.
The scenery is great, perhaps the only good thing about this movie but the bad writing stands out the most. Many action scenes are filled with stupidity, especially the decisions that Jason's character does.
All in all, this is a poor attempt at what could've been a better action movie if directed by someone with a little more experience. It's too long and it made be to fast forward for most of the time. Wouldn't recommend watching it more than once.
