It was a pivotal anime for a few reasons. One of them was that there was a technological change from producing anime with cels that get photographed on a multiplane camera to drawing the "cels" in a computer and compositing them digitally. Haruhi Suzumiya was not the first to be done with CG compositing but it figured out how anime would look with the new technology. So it looks far ahead of older stuff like Sailor Moon but looks behind something like Accel World or Bleach.
Story-wise it was an advance in postmodernization which was already well developed
https://www.amazon.com/Otaku-Database-Animals-Hiroki-Azuma/d...
but it used devices such as telling the story out of order and building systematically on tropes that seemed fresh at the time but now seem cynical to me.
Today they just say "DEI" and expect you to get red in the face like they've been "animalized" in the sense of
https://www.amazon.com/Otaku-Database-Animals-Hiroki-Azuma/d...
Like the Otaku described by Azuma [1] there is a definite regression in terms of the of use of language and ideology, essentially a reversion from a language-using animal which can create unlimited meanings by putting together a finite vocabulary in a grammatical system as opposed to words that have a meaning in and of itself.
For instance, anti-resilience activists will run you out of some communities because you use the word "snowflake" because this is a dog whistle that makes them bark. With their lexicon of triggering words in hand you can talk about the dangers of anti-resilience all day and you're talking right past them.
This style of communication is especially dangerous for marginalized communities because they create a bubble of false consensus that makes them think somebody agrees with them but doesn't do the hard work of explaining themselves and doing the even harder work of bringing about a change of heart across the society would be necessary to do something widespread and durable problems such as the mutual lack of respect between black Americans and the police.
[1] https://www.amazon.com/Otaku-Database-Animals-Hiroki-Azuma/d...