Feedbackz product review tracker which notifies you by email every time there is a new product review on your ASIN.
You'll find this under Reputation up at the top navigation. You'll want to first add your ASIN that you want to track under the Manage link on the left (note: use just the parent ASINs).
And then you'll want to turn on the email notifications under the Alerts link on the left. Select to be notified for only product reviews that fall within a certain star rating and you are all set.
Any new reviews regardless of star rating will appear inside the app here, but only those that fit that criteria you set in Alerts will be emailed to you.