Typically people who write reviews either have something highly critical to write or they have been overwhelmed by a wonderful experience. I am just detailing our experience with Costa Serena to help you decide whether or not cruising is for you and give some (hopefully useful) advice.
We are in our 30s and have always loved the idea of getting a taster of many places without the hassle of travelling. I had always been nervous of sea sickness (occasionally getting motion sickness when in the back of a car) so avoided boats. My husband convinced me that the boat was so huge that I wouldn't feel anything at all. He was right!
The Ship The Costa Serena is huge. It carries approx 4,000 people, 1,000 of which are staff. It is an italian cruise ship so do expect to hear a lot of Italian spoken. I loved this as it made me feel like I was truly on holiday. The ship mainly carries Italian, Spanish, German, French and British passengers and so in order to cater for everyone announcements are made in all languages (thankfully not in the cabin). If you wanted to escape there were always lounges, decks or areas around the ship away from people and noise.