Ohana is a "great value" in the sense that for a fixed price, it provides all-you-can-eat, including select alcohol, all for a fairly affordable price. In that sense, especially for a large eater, or someone who wants a beer with dinner, it's a great value, on or off the dining plan.
When on the DDP, in terms of pure dollars and cents, it's a slight value. If you get dinner at Ohana, with an average prices CS and average priced snack, you may save $2-4 per adult for a day.
In terms of pure dollar value, the best TS values are where there are $30+ entrees that you plan on ordering.