My experience with judging has been positive. The comments always include something positive and then it may have needs improvement in.... I have won ribbons. Bear in mind that sometimes there aren't many entries in a given category and a quilt may ribbon because it doesn't have competition. I try to take my ribbons when they come with a grain of salt especially the blue ribbon I got in a category that only had 3 entries. One quilt that I did the quilting on won viewers choice and 2nd place. The first place quilt wasn't nearly as striking or labor intensive but the judge said she liked mitered corners and all the blocks in the first place quilt had mitered corners done well.
Have fun and be judged if you'd like an opinion on what you can improve.