Honestly I think this is a good thing. I would rather they remake all of the textures under one style so that the game feels more unified, rather than keeping them as they are. If you don't like some (or all) of the new textures, then use a resource pack to change those. I like most of the previewed textures, but I will most definitely be using the old cobblestone textures as well as slightly tweaking some of the new ones.
I think it is a good change overall. It's better that the default textures all fit one style. Resource packs will always be there to revert individual textures you don't like, similar to how "old sounds" resource packs exist to revert the changes in sound made to the game in 1.4.