I'd probably use a temp table for that, rather than a case.

  begin;
  select id, new_rating into temp_ratings values (1,25),(2,94),(3,16);
  update table place set rating=new_rating
    from temp_ratings
    where place.id=temp_ratings.id;
  drop table temp_ratings;
  commit;

Scales well, and almost all db engines know how to do that join. You can index the id, or use a temp table, or whatever depending on the shape and quantity of your data.

(edit -- actually finished the post)