I can't say I've heard of it, what's it about?
I think I might have problems answering that question.
Lain starts off with a suicide of a girl. A few days later, all of her classmates start to receive e-mails from her, even though she's dead. (Note that the anime was made in 1998, when e-mails were a bit harder to fake, so this is more dramatic than it seems nowadays)
Most of them dismiss it as some sort of a cruel prank, though it does bring someone to tears.
Enter main protagonist Lain Iwakura, a shy loner. "Not in the "I play World of Warcraft all day and I have no friends" way" (quote from GRArkada's review), no. Just a fairly normal shy loner who isn't that good with computers, either... but, since this anime is big on cyberpunk, it doesn't stay that way for long.
So this whole situation intrigues Lain and she starts actually
using her e-mail, specifically, to communicate with this... person, whoever he or she maybe. So, Lain gets told by that girl that she only abandoned her body and in The Wired (=their Internet) she has found God.
After that, I can't describe much because it gets weirder and weirder. The whole way through, it's dramatic, intriguing, stylized, cool and creepy. Lain gets to find out about several personalities of her that act independently, one of them has apparently
always existed in the Wired, and things just go stranger from there. "Due to problems with the space-time continuum you may receive this message tomorrow, or even yesterday". How awesome is that?
Mind you, the first two episodes are a bit slow dramatically, but the end of episode 2 is, IMO, when the series absolutely explodes into EPIC.
TL;DR: Basically, Serial Experiments Lain = ALL OF MY
WHAT