/shrug.
On any disgruntled Cabin in the Woods viewers: Honestly, if you walked into that movie expecting a serious horror film, after the previews that have been shown to date, you probably deserve to be disappointed. You are roughly on the same level a few of the people who were in the theater when I first saw the Fellowship of the Ring, who cried out "That's it?!?!" at the end, and walked out muttering how that ending was BS.
On the nature of Cabin in the Woods: I can see the argument that Cabin is, in some ways, a castigation of the expectations of fandom when it comes to their medium of choice. It could also simply be a way to make a self-referential horror film without making it silly like, say, the Scream or (even worse) Scary Movie franchise.
On the parallels with the Re-Take ME3 movement... /sigh. For some reason, whenever the topic comes up, I have this image in my head that harkens back to an earlier example in this post. Specifically, of someone getting to the end of Return of the King, and exclaiming "That's BULLSHIT! My Frodo would never have succumbed to the power of the ring! And what's all this crap about Gollum going all evil on me again, I made all the right choices!!"
Yeah.
Bear in mind that I agree with the general discontent about lack of resolution at the end; it's abrupt, and I'd really like to know what the consequences of my choices in ME3 lead up to in regards to things like the Genophage, Quarians/Geth, and so on.
But I think the majority of the other complaints are a bit hollow. Particularly the Deus Ex Machina complaints, since in that case people are simply complaining that they didn't get the Deus Ex Machina that they wanted. Bioware has made it pretty clear through the entire series that a conventional victory against the Reapers was impossible.