Amazing. A very original scenario, perfectly executed until the end. It all makes sense, but still leaves a lot of open questions for your imagination.

The main actors are ok, they do the job, but the supporting ones are amazing. The whole beginning sequence with Martin is so weird and hilarious, a perfect intro into the movie. The kid is also creepy as fuck, with a little help from voice over he's just perfect.

The design of the house is also the perfect fit of trying to create something ideal but with no understanding of how things are supposed to be, the whole thing is uncanny valley to the max, just as much as Martin is.

And the whole situation raises lots of questions, what's the correct behavior ? It's rapidly obvious that [spoiler]the kid is not human[/spoiler], so what do you do ? Can you trust them ? Are you sure you'll be released ? Are you helping [spoiler]an alien invasion[/spoiler] or something like that ? Should you not stop it ? Or maybe the other way around, if you manage to raise the kid normally, with love and everything, there's a chance it would end up being a good thing ?
What if you [spoiler]killed it[/spoiler] ? So many other scenarios to try other than the one chosen by the characters.

Do everybody behave the same way ? [spoiler]Does everybody dig their own grave ?[/spoiler] How many instances ? How many time did this happen ?

So yeah, not only is this a very original, complete and captivating story, the whole concept is just genious and leave so many other possibilities to think about when the movie ends. It's new, it's weird, it's fun. Definitely a masterpiece.