Why all the hate? Who knows, really. Go read my reviews, you'll see that I love sci-fi. Particularly of the low-budget kind, so "sum1" is right up my alley. Is it mind-blowing? Nope. Is it fast-paced? Nope. But I don't mind slow-paced movies, so it held my interest, and the tension really ratchets up as it goes along. I also have a fondness for rats, so that may help too. They make great pets actually,. Though they are indeed smelly.
I can't say much about the plot, only that it is well enough executed, and well-paced. If you don't like single location movies with a slower plot, why would you watch this? I recommend that you don't. I will say, I was wrong in my guess at how it would end, and as another viewer said, there aren't many choices. It is a mystery, and it does well at that. It doesn't over explain things, and it leaves a lot of questions by the end. It answers enough of those questions, however, that I feel it satisfies the mystery that was built up.
The acting is well-done, so no faults there. The script is good enough, the sets are well-done, the cinematography is good, sound is good, technically, this is a good movie. Your enjoyment of it, again will hinge on whether you enjoy movies that are in one location, with very little seemingly happening, if you're not, I'd avoid this one.