What is considered grounds to report a review?

Is it just stuff like offensive language? 

Basically, I have a review that states 'I can't give a fair opinion because I hate the MC. I only read the first few chapters'. But they have left a detailed review. This is obviously having a rather negative impact on the ratings just because of some bias. Is this reportable?

Edit: I also contacted the reviewer politely by PM to see if I could talk about these concerns, but have had no reply.
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