The CMS today is really, really risky to work in, since there is no way to roll back any changes to content. We have had incidents where editors have made mistakes, which have taken as lot of time to correct. Database rollbacks, hours of manual work, etcetera.
It must have a version control / history, so simple mistakes can be corrected easily.
Some must have features:
View history (different versions), including username and timestamp
View page in specific version (as visitor)
Roll back edit mode to specific version - and the publish as usual if needed
Nice-to-have:
Side-by-side comparison of different versions