As you may have seen already, over the last week a new update has been rolled out: version 5.8 with Personal Ratings!
With Ratings in BG Stats you will be able to rate games, as well as filter and sort on your own ratings.
If you have Collection sync enabled your rating will automatically be synced with BGG as well.
You can find all information about Ratings here: Rating Games
Enabling Ratings
If you haven’t done so already, you can read how to enable Ratings here: Enabling Personal Ratings