I made our reservation prior to arrival 4 years ago, it was very good, and the food was excellent, get down to the queue area about 5pm they say after 5:30, but there was lots of people there when we got down, so get down early and register your name.
The last 3 years ,they have been offering the Luau to me at RPR , but did not bother, considering doing it again when we are there next week, but if its not available , its no big deal.