It's something so simple that they made complex. It's not just code formatting, even things like italics are annoying to escape from if you're used to the old interface.

Also, I totally understand their desire to get rid of the subdomain aspect of slack. As a developer I get it, I really do, but now there is no way to easily go in the browser to the slack that you want. It used to autocomplete now I have to figure out which slack is what and I get confused.