I fudging love Centerparcs. It's perfect if you've got kids and you come back more knackered than you went but really feel like you've had a productive time rather than just lying around in the sun (which I'm not a fan of anyway).
I agree about taking food with you (including BBQ stuff as all the cabins have an outdoor one).
Book as much as you can before you go, bikes, evening meal or two, activities for the kids - of which I would recommend;
Badminton, ten pin, rock climbing, archery, pottery painting, tree climbing (like an assault course high up in the trees), lake based stuff like pedalos/canoes.
It IS expensive but we actually spend a lot of time swimming and biking which is free once you've hired the bikes.
If you want a game of golf away from the kids they've got a good course at Elveden (which I presume is the one you're looking at being in Suffolk?) and there's a spa and brick like that for the wife. We've done the Lake District one as well but Elveden is our favourite.
The accommodation varies greatly but even bottom of the range is pretty good. We kind of go middle of the range.
It's good because once you empty the car everyone has to park outside of the site so from Fri/Mon evening onwards you really can just bike anywhere without fear of vehicles (with the kids).
I agree also with going later for the swimming. It can be a lot quieter plus it's nice to get in the water after a day of doing active stuff. My daughter often wanted to go twice a day which is a bonus being one of the free things.
I dunno, I like holidaying in this country and as the whole family have fun it's perfect for us.