Back in 1992, Marine World/Africa USA was one of my favorite parks. At that time, I lived in Monterey, CA, and whenever friends or relatives from out of state would visit, I would insist that they saw the park. Such would not be the case today. I've lived in the mid-west since the late '90s, so when I made a trip to Sacramento last week to visit my girlfriend and her 16-year-old daughter, I looked forward to introducing them to the park (now called Six Flags Discovery Kingdom). I was quite disappointed.
For the three of us to park and enter the gate (with tickets bought online in advance), the cost for the three of us was $150, which really isn't terrible when compared with the cost of other theme parks. Once inside, you can count on paying $5 for a soda, $5 for a small ice cream cone, and $12-$15 for a plate of food. Those are terrible prices, but commensurate with other theme parks. (Oh, we went on a Saturday, and there was a healthy line--30-40 minutes--for every eating establishment, so plan accordingly.) My primary complaints, however, are about the cleanliness of the park (which was poor, even by carnival standards) and the customer service (you were lucky if you received a blank stare and an uninspired "May I help you?).
If you have a large family, you may find it hard to navigate the park in one day. I would recommend taking 10 minutes upon entering the park to plan your day (as the showtimes for the animal shows vary): Pick out the major shows you want to see, and then fill in the time around those shows by taking in a ride or visiting one of the many "walk through" animal exhibits. (Unless you fork-over the extra money to get a "Flash Pass," you probably won't have time to squeeze in more than one ride between showtimes.) The dolphin show and the tiger show are must-sees. Back in the early '90s the killer whale show was also a must-see, but they do not appear to have a killer whale exhibit anymore (though the stadium still remains).
One final note about the gift shops: Their prices were not as exorbitantly priced as one might think. If desired, you could easily pick up a memento in the $15-$20 range.
All in all, I'd say low expectations are the key to a good day at this park.
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