Have you ever picked up a show based solely on the OP or ED, without knowing anything about the plot or setting?
Comfy, cheerful, or somber theme - enjoyable visuals/animation; anything's fine as long as it got you watching the show.
https://www.youtube.com/watch?v=MN_WgwEmRaw
https://www.youtube.com/watch?v=fwKeGKYVjTM
https://www.youtube.com/watch?v=GNwxqaWO43k
Yes, NGE
more likely to check out an anime from an AMV