So, this doesn't have the best translation to English, but it's probably the most useful Japanese perspective on why Evangelion was such a revolutionary work for its time. It contextualizes the series as a cultural event and shows how Anno compares with the other convention-breaking directors of that era.
Keep in mind that Azuma has his own slant as something of a pop philosopher in Japan, but I think he nails exactly what made Evangelion a surprise and a trendsetter.
Let me know if you enjoyed the article—I can post more links on useful reading or you can PM me for more.
If you have a lot of free time, I have an anthology of mostly out-of-universe discussions by people directly or indirectly involved in Evangelion from 1994 on: https://www.gwern.net/otaku
Pretty much everything I'd point you to is all in here (thanks gwern, the fandom truly doesn't deserve you).
I highly recommend the 1996 interview with Toshio Okada for a perspective on Anno's mindset, the history of the medium, and the uniqueness of the work.
Also read Azuma's interviews with Anno and especially with Krystian Wozniki--these are very illuminating and will recontextualize your views of Okada and the show as a whole.
If you can hold all of these views in mind, you'll start to understand how Evangelion absorbed so much cinematic power from its cultural moment and forebears. It's a culmination of the medium in some ways. That it did all this while remaining an intensely personal work with an auteur's sense of vision and originality makes it that much more impressive.
http://www.ntticc.or.jp/pub/ic_mag/ic018/intercity/higashi_E...
Keep in mind that Azuma has his own slant as something of a pop philosopher in Japan, but I think he nails exactly what made Evangelion a surprise and a trendsetter.
Let me know if you enjoyed the article—I can post more links on useful reading or you can PM me for more.