If you're talking about the one in Devon, not personally, but my friend took her sons whilst on holiday. She thought it was a rip off, expensive to get in, additional payment required for some activities and rubbish food on sale (it was not permitted to take in your own picnic). So all in all, she certainly would not recommend it.
I went to the one in the North East last year and had a whale of a time! Mind you, we were the only couple there on our own without kids. But the kids looked to be enjoying themselves too. I would agree with the comment above about the food - it was horrible! Next time we're taking sarnies (lots of others had a packed lunch and were eating them in full view of the staff without any reprecussions). I would say it's worth splashing out on because you want to make sure you don't run out of tokens or whatever they're called, and can go on everything without any limits. We had a day ticket each.