There was nothing special about Luna Park in Sydney for us. In fact, it wasn't on one of our places to visit. We only came to Luna Park because we wanted to take a ferry ride under the Harbour Bridge and Luna Park was just the first stop where we could go back to Circular Quay after getting what we wanted to get out of the ferry.
There isn't much for "big adults" (obviously); however, it's good to be able to cross off the list one of Sydney's "iconic" attractions. When we looked around, although there was no entrance fee, the fee for each ride was considerably pricey.
All in all, it's good for an iconic picture at the entrance of the park - something iconic and uniquely Sydney in itself. If I had kids, based on the costs of the rides, how dirty it is, and "accompanying adults" having to pay extra, there are other places I'd probably take them.
Staff were helpful nevertheless, my girlfriend and I were approached numerous times by friendly staff members who thought we had lost our child.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.