RSS - that is properly formatted, not like the old blog which just ignores all formatting and looks like a giant paragraph.
Commenting without becoming a member, comment moderation.
The ability to resize the blog and design a sidebar, or putting in a layout that has a sidebar in it.
Wix code with Wix Blog
Ability to add call to action buttons in blog posts
Ability to embed wix stores catalouge, wix video
Over all speed.