Is it free dining? Or just a package that includes the dining plan? A free dining offer is essentially WDW paying for the dining plan out of their profits. As you need to pay full price for the room, it's essentially covered (to a point) by not giving you a room discount. So in theory once the deal is over the package would cost the same, just not include dining.
If it is a good deal or not is really specific to you. If you are from the UK you may have access to other discounts/packages that could be a better deal if free dining doesn't appeal. Depending on your party size and resort class, a party of 2 might save more taking a room discount at a deluxe resort than by taking free dining, but a party of 4 staying at a value might save more with free dining over a room discount. And I believe that some UK agents can get good rates on the overall package by guaranteeing certain numbers of rooms/plane tickets sold. But those are packages that the TA puts together, and not rates from WDW themselves. Check the numbers on the WDW site itself and see how it compares.