We travel fairly regularly on The Spirit of Tasmania and are always keen to book a table. The menu is a fixed price for two or three courses and unless you're really hungry it's good to share an entree and dessert thereby only paying for two courses.
The steak is great, cooked exactly to order, in our case warm blue. It was melt in your mouth tender and flavoursome. The duck Asian salad was a nice ballad with the Asian flavours cutting the richness of the duck - of which there was plenty.
Staff are always very helpful and generally knowledgable about your destination.
Ask for a table inside the restaurant - there are table in the aisle which aren't very private.