Do not read my review if you intend to watch the film
Firstly, there IS and ending to the film; and anyone who reviewed this stating there wasn't simply didn't understand the twist at the end. The twist? Yep, a twist - and here it was that the film starts in the same place it ends. Now, personally, I didn't see this coming and, subsequently, found this to be pretty cool.
I will concede that the constant rain in the film is a bit of a mystery and wasn't necessary to the plot. It was a poor choice by the director to do this. As for the absence of parents... I have no idea why anyone reviewing found this to be a surprise. Absentee parenting is very common. Just assume that these parents don't care about their children, and the lack of parental supervision becomes unimportant.
I think there were some cuts made to the film which made the middle section - where lots of chain emails were flying around from person to person - seem a bit muddled. You didn't know why the same person was getting the same email over and over again...unless you listened. The same applied to the motivation of the killer. In both cases the reason is in the film; you just have to listen to hear it.
The appearance of the killer is not explained though. Thankfully, I'm not one of those people who needs everything spelt out for me, so this didn't particularly bother me. I can make some assumptions. Also, I think the makers were hoping for a sequel, so they'd probably have explained it then.
A couple of the deaths in this film were very gory and easily a match for anything in the SAW franchise.
Overall, I enjoyed the film; and, in some ways, I wish I hadn't read all the negative reviews because then I would have seen it sooner.
I bought the blu-ray (for £4 from CeX) and the picture and sound quality were excellent. Only a trailer for extras, though.