What is Serial Experiments Lain about?
At first, I flagged this as opinion based. However I remembered seeing an interview with the producer, director and writer a long time ago and was able to find it.

There are a few pages of interview on that site, but I have quoted the most relevant material here. 


  [Writer] Konaka: There's not a particular message about technology. Technology advances anyway. [...]





  [Producer] Ueda: [...] This work itself is a sort of cultural war against American culture and the American sense of values we adopted after WW II. [...]





  [Interviewer] Q: Does the series have a "message"?
   Ueda: The message is, Things are simple.


This is probably the only English language interview. I definitely wouldn't take what they say at face value.