Scott Wise’s review published on Letterboxd :
The level of bravery on display in this film is nothing short of staggering. Shane Carruth weaves a complicated, densely layered narrative with a completely unified and incredibly beautiful vision. As writer, director, cinematographer, actor and even composer, that's an incredibly daunting undertaking for any artist, and in lesser hands could easily have seen it devolve into a broken mess of a superfluous art flick, which Upstream Color is certainly not.
I loved his last film, Primer, for its (perhaps more) intricate and opaque narrative. But it did feel like a freshman release to this much more polished sophomoric output. Carruth really seems to have mastered every single one of the roles he plays on this film, with a performance to match Amy Seimetz's inspired presence. The protagonists are at once frustratingly distant and symbiotically connected, which makes for a truly original exploration of two people finding each other.
Beautifully compelling abstract sequences and a surreal exploration of what connectivity means (including through at least one grotesque vignette) are all that connect this film to the genre of sci-fi. And that's why this film is difficult to interpret. It doesn't feel like a sci-fi film, but it's underlying story - although never clear and perhaps open for interpretation - feels as though it is told as much through symbolism and allegory as it is expressly alien in nature.
Like Primer, this is a film that will stick in your head and keep you thinking about it for weeks and months after you watch it. It is intensely emotional and evokes the same sort feelings I have upon watching Terrence Malick's work - rich in visual beauty and viscerally emotive despite a narrative that doesn't seem to be able to fit within the frame.