Let's put aside the fact that there are some people who find fault with everything. There are indeed rational people who have had negative experiences and post them to make others aware.
The important thing is not to get excited over one bad review, but to watch for a trend. Knowing what some people didn't like about something can actually help you avoid it when you are on your cruise.
Every ship and every line has good weeks and bad weeks in certain areas. A bad review this week could actually be a positive thing because it gives the line a chance to correct it for the next. Keep in mind that the cruise lines pay close attention to what is said on these boards and if they read bad reviews they will definitely look into it!
We always say, a bad review is an opportunity... not a death sentence.
I live in Warnemünde and had passengers last week from the Jewel on my tour and THEY LOVED IT! They were having a grand time and said that everything onboard was fantastic and the ship was lovely.
So...from their mouths to mine... go and have a great time!