If I read one negative review of your hotel where the majority were favorable, I would discount or ignore the one bad review. However, I have seen reviews on TA where the majority are negative and would believe that a hotel operator, who either ignores problems or does not respond appropriately to the reviews, should suffer the consequences. Additionally, suing for slander opens up other sites (e.g. Yelp, Zagat...) to the same issues in a world already overwhelmed by lawsuits.

I hope your situation is resolved to your satisfaction.