We love Center Parcs. We have just come back from a midweek break and immediately booked for the same time next year.
Yes the activities are slightly more expensive than at home, but not excessively so. DS1 did a morning each of cricket, tennis and soccer school. DS2 did both archery and fencing with DH. DD went on the Teddy Bear's Picnic and on the Children's Pony Ride. All 3 DC went to the Party Hour at the Time Out Club. I think we spent about £100 on activities altogether.
We spent every afternoon in the pool, which was free. The DC also spent a lot of time in the parks and soft play areas, which were also free.
The food in some places is a bit pricey, but in others it is very reasonable. One night we ate at Huck's, which was fairly expensive but very nice. The next night we went to the Sports Bar where Burgers were BOGOF, so that was quite cheap. We had the carvery at the Pancake House, which I thought was a bit over rated as there wasn't much choice of meat and veg, but DH really enjoyed it. We had pizzas from Dining In one night which were very reasonable, about £7 for a 12". On the last night we ate at The Forester's Inn, which was very nice. The children's meals were lovely and the adult meals were very well priced, I think my main cost about £7.
The DC are already planning which activities they want to do next year. I love the fact that all 5 of us can find something to do which interests us there.