I think every review must be taken as one person's opinion, whether that be a regular user or paid reviewer, everyone has their biases, some intentional, some unintentional, collectively user reviews can be helpful but even that is not infallible, that's why it's important to get as many different opinions as possible from as many sources as possible, if your on the fence about something. With review bombing, both negative and in the case with Ubisoft and Assasin's Creed Unity, positive, reviews might not always be indicative of the game itself, but of the company or companies behind it, so take each review individually and see if they have valid reasoning for their review, mostly any "review bombed" review can be easily identified, so if the reasons behind a game being review bombed aren't a concern to you, then ignore those reviews.
As for the practice of review bombing, mostly of which is used negatively, i understand and like the idea of customers having a voice, and it has an effect to be sure, it also does help make others aware if there are some major issues, they might not have been aware of, but it also does make it more difficult for those who might not care about the issues, so perhaps there is a better way to be heard, i don't know, but it does work, as it hurts the bottom line when users are turned away by the bad reviews, and that's what companies tend to listen to, anything that hurts the bottom line. So, I think that is important too.