Kristhian Morales’s review published on Letterboxd :
Shane's Carruth's lo-fi, time travel movie has been lauded as a modern sci-fi masterpiece and with reason. Primer, which was produced for $7000, arrived at a time when science fiction movies had abandoned big ideas for high budgets and special effects: their intent was to stimulate our senses but not our mind. Primer has been accused of perhaps going too far in the opposite direction with a plot that folds in on itself so many times that by the end of the film, and even after many viewings, one remains unsure of how many permutations of the characters and events we have seen. I won't pretend to understand exactly what happens in the film, but every time I watch it I get a better sense of what is happening and when it is happening. However, the pleasures of Primer are as much about experiencing the mystifying nature of discovery as they are about figuring things out.
The plot is fairly straightforward, until it isn't: Aaron and Abe, engineers working out of their garage hoping to invent the next big thing, accidentally create a time traveling machine and go about exploring how it works and how they can use it to their advantage. Carruth uses dialogue in the early scenes filled with scientific jargon while making no attempt at handholding the audience. It takes a few minutes to get used to, but it lends an air of authenticity to this world and establishes the character traits of Aaron (impulsive, professionally frustrated) and Abe (careful, inquisitive, honest) surprisingly well. The opening sequence, which tracks a conversation through several shots and locations uses clever editing and dialogue to ease us into the film. It works as table-setting and showcases an understanding of cinematic language often missing from first time features. This sequence also provides us with a feeling of ease that is later disrupted by a more abrupt, fragmented editing style in the second half of the film.
Eventually, Aaron and Abe start using the machine to travel back in time and get rich by playing the stock market. Everything seems to be going well until they begin keeping secrets from each other and start traveling back further in time and more often, their friendship slowly falling apart. We revisit scenes we had seen before from a new perspective, which invites us to question everything we have seen up to this point. The last act of the movie is a head-scratcher, with doubles from different timelines coming in contact with each other and Aaron and Abe's relationship growing more and more strained as their true natures (or at least one of their many natures, given the multiple timelines) are revealed by how they deal with their newfound abilities.
Watching Carruth pull it off is a dizzying, exciting experience, but the resolution of the character journeys at the end of the film feels rushed and unsatisfying. By the nature of the film we only see a fraction of what the characters experience, which means that the definitive split between the two friends and Aaron's decision to leave everything behind, including his family, makes sense if you take into account that Aaron has experienced up to two months of time over the 5 days in which the movie takes place. But we only see a few minutes of that, which means that his decision at the end of the film feels unearned, at least to me. Nonetheless, Primer resonates on a thematic level as it declares that our weakness and insecurities are more dangerous to our well-being than any technology could ever be. The delivery system is as complex as they get, but the simplicity of that message is what makes Primer worth our time.