Modern magic.
Magic as a substitute/parastitute/branch for technology and science is a big turn-off for me. I like magic to be mysterious and rare in the world.* Eberron appears to lean into modern magic and I'm not willing to spend $25 on a book I likely won't like.^ I don't really care for...
I use my own world of Everbee. Right now we are in the Isian area which is mostly underground--so, my version of the Underdark.
I have areas (Lamothe) where things are very gothic and areas (Naphtali) where things are very Indian. Chrysi where it's Roman, Maighdine and Lyonaighe where it's...