I just stumbled over this suggestion. It appears all those bullet points have already been addressed in their own suggestion threads.
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add own reviews
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different rating range → 10 Star ratings (half stars)
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edit watch history
- delete wrong watch events from history → Plex Dash is your friend
- you can set/change watched-date using the Activity Feed → https://support.plex.tv/articles/activity-feed/
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Custom tags → Custom video tags
Side note: The examples you’ve mentioned could perfectly well be collections; if you don’t like them to clutter your main library, simply set them to be hidden, this way they’ll only show on theCollectionstab.
I’ll therefore close this thread as duplicate(s)/implemented