Loin of young wallaby is delicious; it's a wee bit gamey (but only enough to differentiate it from 'domestic' meats) and slightly fibrous in texture somewhat like lamb but darker - a bit more similar in texture to young camel, if anyone's had that, but obviously very different in cut. Roo steaks can be good, too - depends on the age and type of roo.
Anyone eating roo sausages or burgers in a restaurant or from a supermarket is risking a tough dry gamey old boots experience; you might be lucky or you might not. Unless you personally know who's shot them, the meat might well be (often is) from the toughest bits of the biggest - hence oldest - animals.
On stations (farms) where it's not sold off the farm, or only to locals, the big old roo's carcases are usually used for feeding the dogs. It's a bit like really old mutton without any fat content!
Roo hunters licensed for general meat sales for human consumption obviously want to get the best returns possible for their investment in not just the shooting, but also the butchery, so joints from old animals which pass the inspections will of course be sold on commercially.