Fire has always been my #1 concern on a cruise ships. That's why I won't go unless I can book a cabin with a balcony.

People who 'cruise on the cheap' say that they really don't spend much time in their cabin. That's because they are usually very small. If you are over 6' prepare to be uncomfortable if you cruise steerage class. Not to mention water sloshing on the port hole can be unsettling if you are lucky enough to have one.

Also, older cruise ships can get a little ripe with mold operating in the tropics. Fresh air is always a nice upgrade.