There seems to be a wide variation in the reviews of this movie, either people love it and give it a 8+ or hate it and give it a 1.
When going into this movie you need to keep in mind it is a low budget Australian independent film. The fact it's Australian is important as low budget American films are usually between 5 - 10 million whereas that's a big budget for an Aussie film. This movie cost less then 500 000 dollars to make so you aren't going to get A grade acting. The special effects are very good and the script isn't too bad (though has a few Aussie things said/happening that non australians may not get).
I enjoyed watching this film. Yes the acting was cringeworthy at times but, as a father of young kids, I could relate to what was going through the father's head and it was thought-provoking for myself and my wife as we discussed how far we would go and how we would react in that situation.
Considering some of the overblown ratings for some really bad big budget movies on this site, I would recommend you give this one a go especially if you are a parent.