First of all, let me state something that nobody seems to want to say explicitly; this is one unnerving movie with some of the most unpleasant scenes I've ever seen, and that includes Cronenberg. Also, there's an undeniable homoerotic subtext to the whole thing (and I'm not inferring; it's pretty clear, despite the lousy subtitle job Image subcontracted out.)
As far as comparisons go, this is a lot like the work of Jan Svankmajer, in terms of effects and narrative feel (and I suspect Tsukamoto knows the work of Svankmajer well.) But the material is about as far from Svankmajer's social concerns as you can get.
I don't claim to know Japanese society that well, but I DO know it wasn't (and still isn't) nearly as tolerant as the US, and "Tetsuo" is a strong reflection of that. The main character is a man who is torn apart by guilt over a crime he has committed, and also for his failure to conform to societal standards. He is terrified of women, and he also resents them (epitomized in two extremely gory and unnerving scenes.) And because, one feels, that he's told that he's unnatural and inhuman, he BECOMES unnatural and inhuman, literally an iron man.
This is not a upbeat story; this is a story about a man who has destroyed himself and achieves the power to take the society that caused it down with him. Even finding love isn't enough for him. This is a movie about a man who is twisted and warped by society, and who will destroy everyone thanks to that society.
Personally, I found it fascinating, but unless you've explored Jan Svankmajer, David Cronenberg, David Lynch, and others extensively, I would be careful about approaching this. Put it this way; if you weren't bugged by "Crash" but found it interesting, "Tetsuo" won't be too much for you.