The reality is that there are people who hate everything and everything that isn't perfect is a problem for them. Then there are those where everything is perfect and they'll overlook a boatload of issues because they are overly forgiving.
That said you have to read between the lines and look for trends. Two bad reviews out of 10 that have 8 glowing reviews probably suggests that the park is fine. If there are only a couple of conflicting reviews, you have to dig deeper. There are many places that people post reviews.
We've found online reviews to be very helpful.