I agree the zoo gives Chessington an advantage the other parks are lacking. I can't take family to Thorpe now that they've removed the toddler specific rides, which means I don't go. But all the family can be thoroughly amused in the zoo and of course it's a great place to pass time while you're waiting for something else. Plus, with the zoo being open in winter and the additional rides they've been opening along with it we're getting to a point where we have a year round theme park.