Whenever you read a review on line you have to question the motives and competence of the reviewer. For some people, everything new (or everything they own) is brilliant, perhaps because their experience is rather limited. Others might be used to only the very finest, so everything else is rubbish in comparison. Some folks are overly positive, some overly negative. All that is before you get to the distinctly uneducated, attention seekers or those that are just plain old vindictive.
However, you've also got to accept that we don't all share the same tastes.
Whilst I wouldn't take to the net to rubbish my local pub, I don't care for it much, and wouldn't bat an eyelid if it shut down. I'm not particularly averse to pubs, but they don't loom large in my life. I'm quite sure that lots of people love it, but me not liking it doesn't make me wrong. It can still be a perfectly good pub, that many enjoy, despite me not liking it. Not that I would, but if I reviewed the best sushi restaurant in the world, I doubt it would be the greatest review ever, I simply don't like sushi.
Then you must consider that all else could be as equal as possible yet we might still have a different experience. At any single restaurant, on any single evening, two different people may experience different levels of service, even if the same people attend them. One goes away thinking the place was great, the other thinks it rubbish. Both may be right.