It's so visually striking that you could never fully describe Tetsuo in words. But here are a few that apply: Japanese, hyperactive, perverse, industrial, surreal, Faustian bargain, contrasty, black-and-white, Kafkaesque, scifi, stop-motion, manga-influenced, revenge, technology, alienation, supervillains.
Shinya Tsukamoto is an actor (he's the antagonistic "Metals Fetishist" here as well as Jijii in Ichi the Killer) as well as a ground-breaking writer/director/cinematographer. Tetsuo's influence can be seen clearly in directors as diverse as Darren Aronofsky, Takashi Miike, and even David Cronenberg.
There is definitely a plot, but due to the non-linear editing and sparsity of dialogue you'll need to pay close attention on a first viewing or else you'll be overwhelmed by the engrossing visual style (which might be a good thing). It's filmed in contrasty black-and-white. Each frame is cramped and chaotic, much of the time it's filled with wires, pipes, chain-link fences, and all the other incidental debris of life in the late 20th century... which suddenly seems significant and even menacing.
Towards the fifty-minute mark (it's 67 min. total) the willful excess starts to feel a little too excessive, perhaps the manga influence is a bit too strong. But Tetsuo finishes strong, with an end that's at once unexpected and inevitable. Highly recommended.