The anime is an interesting deconstruction of the mecha genre; it stops to consider what it might be like for child soldiers to enter the battlefield, with humanity's survival riding on their shoulders. Many of the characters are implied to have PTSD and are severely damaged. The three main characters, Shinji, Asuka, and Rei, all face immense psychological obstacles.
Early episodes are somewhat dark and psychological, but with the introduction of Asuka, the series lightens slightly and becomes a little more action-oriented. Beginning with episode 16, the show becomes more and more psychological and experimental. Due to restrictions, many plotlines, concepts, and character points are left unresolved, and at times pacing seems off. The last two episodes are extremely unconventional and many viewers are likely to find them disagreeable; End of Evangelion is meant to provide an alternate ending.
One note to women viewers: there are some very 'fanservice-y' or objectifying scenes throughout the anime, which may be uncomfortable. This generally lessens in the later portion of the anime.
