We did the Adventure Express in March and were very pleased. It is expensive, though, so you have to determine for yourself whether the benefits are worth the cost to you personally. I think the value increases with the crowdedness and heat of the park. For us, not having to wait in line for Kraken, etc. and getting excellent reserved seating at the shows with no waiting was very worthwhile. The "behind the scenes" part of the day was a nice extra, but nothing overwhelming--for example, we got to pet a penguin and toured the shark tank from above (pretty cool, actually). A very tasty lunch was brought to us in a reserved section of the cafeteria--again, no waiting. The tour guide will answer all your questions and shepherd you around efficiently--no wasting time poring over maps and making wrong turns. If money is no object, definitely do the tour. If money is tight, skip it. In between, it depends on what's important to you.
