This works well, as a tense and claustrophobic little chiller, off-setting the glorious panorama of the Australian outback with the small clearing and tunnel area that the characters find themselves in. The tension begins to build after the leech attack (which is well handled) and doesn't really let up to the end, as the characters go through believable reactions to the circumstances and the growing realisation that this isn't going to end well for any of them. The film is so well constructed that even when not much is happening on screen - the drawing straws scene, for example - you can still feel that we're not dawdling, that a good pace is being maintained.
The actors all acquit themselves well, with the dialogue ringing true and there seems to be a genuine bond amongst the characters, which is good to see. The prosthetic make-up effects work is effective and gruesome but sadly, the same can't be said for the CGI. Whether it be the poorly matched CGI images or ropey green-screen work, it's enough to pull you out of the film for a moment. That gets worse at the climax, where the CGI appears to have been made on a Commodore 64.
That niggle aside (which, depending on your tolerance of poor CGI could be big or small), this is a cracking little film, with believable characters and a great pace, that really builds tension and suspense. I'd recommend it.