1 - A lot of dramatic conflict which wouldn't be resolved in a single episode
2 - There would not be a trace of tweener/valley girl talk.
3 - The art style would appeal to a wide variety of ages and be less of this "super happy American art style (actually done in Korea)" and more of the type with more painted-looking backgrounds, focus on character's eyes, and cuteness.
4 - It would have zappy.
5 - It wouldn't be afraid of its audience not understanding so there'll be deep themes related, usually not in verbose philosophical explorations, but in subtle, quiet ways.
6 - Characters would die but not for any old reason.
7 - It would have unique but not "hip" music.
8 - It would be full of little references which make rewinding and watching it again especially fun but can be completely enjoyed on a surface level.
There are a few things, but that's what important to me. If I were making a Mecchen Anime then I'd have to create a pillow of Katsumi so she can cushion me.