jamb,
After a year of reviewing stories and having my stories reviewed, I learned a few things that helped re-align my perspective, not always, but most of the time.
1. Check the reviewer's ratings for other stories and see if you agreed with some of them. If you see a lot of low scores and the stories have a lot of scores on the high end, rest assured it's not all your writing skills that landed you that number.
2. If the disparity is by a large margin, you could email the person, like Ruby suggested, and politely ask them to re-read the story and adjust the score. The keyword is politely.
3. You can respond politely to the review and say that you will take their remarks under consideration and thank them for reading it.
Nikita