Put simply, this film is mind-blowing, staggering, and amazing. Made for the price of a used car, Shane Carruth's feature debut is a startlingly complex investigation into the realities of time travel. In spite of its modest 74 minutes length, this film had me pondering for days, and I've now seen it four times and am just about confident that I understand the gist of the plot. However, don't let the complexity put you off (and my, but it is complex; Memento and Mulholand Drive pale in comparison), one of the many joys of the film is that you never quite know what's going on, and this puts you in the exact position of the protagonists (there is one event involving a catatonic man which even the director has admitted he has no idea what exactly happened and inserted it purely to show how far out of their depth the characters are). You never feel like you need to work out exactly what happened, and how A got to B and then was in time to visit C, etc, as the central ideas and twists keep you on the edge of your seat.
The good things about this film are really too numerous to go into detail with without writing an essay; suffice to say that the acting is superb and realistic, the dialogue refreshing, the cinematography understated and perfect for the story, the score haunting and effective, the editing skillful, and the re-watchablity infinite.
A couple of things that really make this film one of my favourites of all time - the little details; the characters' ears bleeding for no reason and gradually losing the ability to write after too much time travel, subtle lines like "I haven't eaten since later this afternoon", and the need for oxygen tanks when waiting in the coffin-like homemade time machine 'boxes'.
Apart from including one of the cleverest and intriguing films of all time, another reason to purchase this DVD are the hilarious and informative commentaries with director and crew - never have I heard such honest and insightful commentary, and the crew commentary is side-splittingly funny, stuffed with in jokes from the shoot that you would never dream of hearing about on another film.
Finally, to answer one of the main criticisms the film seems to be getting, that it is too dry, intellectual and lacks any sort of human or emotional side. And this is just a blatant lie. The central crux of the film is the gradual destruction of two friend's relationship as they try to deal with the infinite power and responsibility of time travel. Throughout the film both friends go through subtle and realistic character arcs, one becoming more secretive and distrustful, and the other becoming a lying, controlling bastard.
I really haven't even started explaining the myriad joys of this film (I haven't mentioned the brilliant premise, style and use of tension), but this review is long enough.
Suffice to say, this film simply cannot be missed.