Before going with a CMS, test it!
Is it SEO friendly, ie pretty links
Is the CMS secure? also security features
Allows to create, delete, edit and organize pages (not all cms have that)
Text editor:
Good accessibility and usability
Has good assets' managing:
Search:
Customization:
User interaction plugins: (if needed)
Permissions (multiple roles)
Versioning
Multiple website support (MUST HAVE) eg
Multilingual support