I know it's been a long time, but I want to post a solution here for people in the future.

Instead of the important label, you should use ^iim. https://mail.google.com/mail/feed/atom/^iim

You can find a list of special gmail labels like this here.

I know it's been a long time, but I want to post a solution here for people in the future.

Instead of the important label, you should use ^iim. https://mail.google.com/mail/feed/atom/^iim

This will show a list of emails in your inbox that are unread and marked as important. I have "priority inbox" enabled on my end, not sure if it's necessary for the link to work as expected.

You can find other special gmail labels here.