If Planner is to replace Project/Project for the Web, and we are now 8 years into development, many of these features mentioned by others should already be available. Creating feature disparity/licensing differences among 3 products designed for project management has made choosing which product to use almost impossible. We all need, and quickly, a modern (keep the attention of the newer generation who's going to be using the product), flexible (can be used for simple and complex projects without having an overly complicated entry point) project management too that is well integrated with the Microsoft suite (Outlook, SharePoint, PowerApps). I'll reiterate a few missing features that have caused our organization pain:

  -  The inability to @mention someone in Planner tasks.  @Mention should go to Teams or Outlook or both (configurable maybe?) to we meet the assignee in the communication tool that they use.

  -  Along with this, when Comments are added to a task by another assignee or the PM, that should generate some notification to the assignee(s) in their chosen platform.  Currently, comments go to a Team DL that is not always present in Outlook dending upon how a user has set it up.  And further, if an assignee has not yet commented themselves, they will not be included directly on new comments.
(These two points above make task management very difficult in Planner as people don't get updates/info in a timely manner)

  -  Integration with Roadmap (which could be improved to show impact of delays for instance) for quick executive/team visual reporting.

  -  Inability to embed a Planner project into SharePoint.  We want to use SharePoint as the central place to manage a project, such that any documents, lists, calendars, news, are all accessible from a visually pleasing, well organized, and central location.
(Please integrate SharePoint and Outlook calendars so team calendars can be accessible in Outlook and SharePoint.  Teams/SharePoint integration is not sufficient for the above comment...it is better to work in SharePoint)

  -  Integration with OneNote, such that a task can be easily created from a tag in OneNote.  This is where many organizations keep project notes and updates, so why not?

  -  Establishing dependencies/predecessors in tasks

  -  Gant view, with option to specify at which level, or solid integration and improvements to do this in Roadmap

  -  Ability to mark milestone tasks and tie visualization to Roadmap

  -  %Complete is needed, not just perpetually "in progress"

  -  For the PM, task updates should be more easily visible in Planner.  Recent changes should not be simply highlighted in a thin green line, but filterable...show me all changes in the past X days, for instance.

  -  Ability to add photos, screen clips to tasks without having to save as an attachment.