I've been but must have been about 10 years ago now. I think I was 12 and thought it was a great day. But we were staying in Poitiers (sp?) so it was very near to us.
I'm not sure how easy it would be to do for a day trip from Paris.
Have you been to Parc Asterix? Thats a great day out. Its very close to CDG. We did it last year before our evening flight back home