Vantaggi
Travel. Free food. Free room. Lots of free time. Lots of sun. Fun people. Cheap drinks. Lots of parties. The chance to make friends from all over the world. Gain the perspective of people from many third world countries, who are usually working on the ship under different circumstances than you. Once and a lifetime experiences like skydiving, hiking through the rainforest, snorkeling in the great barrier reef, touring fantastic cities all over the world. Also playing music every day can be fun. You might end up with a great band!
Svantaggi
First off, the lifestyle can wear you out after a long contract. The crew areas are not the same as the guest areas. Extremely small quarters. Tight, bleak hallways, annoying, ever present hum of the ship's machinery. Many of the crew members are rude, unintelligent, and have no social skills. You will not have a lot of privacy. As an orchestra musician you will likely have a roommate, and there are very few areas of the ship to find solitude. Not much room for upward mobility. As a musician, you can move up to musical director, but that's about it, and they make only slightly more money than the regular orchestra musicians. The crew food is often of pretty low quality, and because of cutbacks, is getting worse all the time. The party scene may become overwhelming. Many people working on cruise ships are overgrown high school children, and will need a liver transplant by the time they are 40. ...and probably some therapy. The musicians might not be that great. It's kind of a crap shoot. Best advice I can give: If you have the choice for your first contract, go for a short contract (0-4 months) or a vacation fill.