It's honestly a very interesting movie. Great performances by everyone with a great, dark idea behind the story that will keep you interested to the end. With an acceptable end given the nature of the story. Probably the biggest thing though is that you don't really connect with anyone.
Each character is intentionally gray and I feel that you were suppose to pick one side to go with but in the end you don't really care for either side of the conflict. You don't even care enough to appreciate or enjoy the ends for each character. You just expect them but hope it's done in a creative way. Or done in such a creative way that subverts the end you want for them and you are okay with it. So without any emotional investments in the characters, you are only left with the curiosity of how it will all end.
While funny, the whole idea of the situation holds such a presence that some will feel hard to allow the comedy to set in and meld with the overall dark story. While I say the ending is acceptable, it's also one that will probably disappoint audience the most and might leave some with regrets. Regrets like, that it was amongst a list of acceptable/wanted ends but it being the weakest in the list. Regrets that such an interesting plot had a weak story that leads to a less interesting end. Regrets that such a smart idea had such a simple and displeasing end.