After several episodes were produced, the first episode aired on October 4, 1995, long after originally planned. Initially ignored (although received positively by those Gainax fans invited to early screenings), viewership grew slowly and largely by word of mouth.
The 16th episode marked a distinct shift that would characterize the second half of Evangelion as being more psychological than action or adventure. This change in emphasis was partly due to the development of the story, but also partly because by this point, production had begun running out of funding and failing to meet the schedule; this collapse has been identified by at least one Gainax employee as the impetus for Evangelion's turn into internal conflict:
I didn't mind it. The schedule was an utter disaster and the number of cels plummeted, so there were some places where unfortunately the quality suffered. However, the tension of the staff as we all became more desperate and frenzied certainly showed up in the film … About the time that the production system was completely falling apart, there were some opinions to the effect that, "If we can't do satisfactory work, then what's the point of continuing?" However, I didn't feel that way. My opinion was, "Why don't we show them the entire process including our breakdown."
But nevertheless, by the 18th episode, it had become enough of a sensation that Eva-01's violent rampage "is criticized as being unsuitable on an anime show that is viewed by children", and episode 20 would be similarly criticized for the offscreen depiction of Misato and Ryoji having sex. With this popularity came the first merchandise, "Genesis 0:1" (containing the first two episodes). Beginning a trend, it sold out. As the series concluded on 27 March 1996 with "Take care of yourself", the story apparently remained unresolved: Third Impact and the Human Instrumentality Project are implied to have begun or even finished, but the episodes focus largely on the psychology of the characters, leaving deeply unclear what actually happens. The End of Evangelion was meant to replace or complement the original episodes 25 and 26, in order to better explain the events of the ending.
Read more about this topic: List Of Neon Genesis Evangelion Episodes