Certain aspects of the aliens biology stretched my sense of disbelief too far, it shattered the illusion for me.
And the thing with the child actor and the monkey; I get that it was subtext but if you're also just going to speak the message plainly later on in the movie, it's going to render all of the subtext pointless. Just a bunch of red herring flashback filler that's only connection to the plot is through a secondary character who was less of a character more a literary device to reveal plot details about the alien. Oh and speaking of red herrings, the disfigured lady with the veil from the trailer; showed up for less than 2 minutes to clap and say no lines. Just designed to get you curious enough to buy a ticket. I'm watching it again with friends today I'll try to see if I missed something that ties this mess together but honestly I don't think so.
Tl,dr: it's only good if you don't think about ANYTHING too hard.