New features and enhancements should always be at the top. The main usefulness of release notes for most of us is to keep up with new features and enhancements. Intermingling these with fixed bugs amounts to a denial of service attack on our brains, as we try to pick out the items that are useful to us.
The release notes format has changed many times and will probably continue to change. We used to have this, and it was lost. It should never be lost.
Also: new features whenever possible should be supported by images.