It is a lot of fun. We don't have a Japanese steakhouse in our area so finding one when we travel is always one of our 11yo's top requests, and Disney's is one of the best we've been to.
They cook in front of you on a hot griddle type surface built into the table, and the chef cracks jokes, makes a volcano out of onions, and is generally much more entertaining than waiting for your food at a normal restaurant, so kids tend to enjoy it. The food is simple but very good - grilled meats, veggies, noodles and rice with a trio of sauces served on the side for dipping. It is different enough for adventurous eaters but basic enough that picky eaters won't have a problem either.
If you do go, try the tempura appetizer. It is really yummy!