You don't unzip anything.
The download is the ISO.
If it appears to be a RAR file or similar, it's probably because you've let some 3rd party software take control of your file associations and/or you have the default Windows option of "don't display filetypes"
I'm not sure how to make the answer to this question any clearer, it's currently the very first question & answer in the FAQ, which is linked to in the download link email. It's also explained on the page with burning instructions, which is similarly promoted in the download email. Additionally, clicking the very prominent "Support" link at the top-right of the EasyRE landing page takes you to an annotated "help index" of sorts, the first few links therein also addressing this question.
@Acydikeen I'd appreciate any feedback or insight as to how this remains difficult to find, or advice on what we could have done better to make this information more visible.