Depending on the cruiseline, they can tend to be the smaller of the cabins offered. They are also PITCH BLACK when the lights are out. There is no natural light, so you really can't even see your hand in front of your face. RCCL has an interesting option which is an inside Promonade Cabin. It overlooks the Promonade deck with gives the illusion of being somewhat outside and you get a window so it at least lets some light in.

Personally, I am claustrophobic so I can't ever get an inside.