Games are sent first based on availability then by the order they are in your GameQ.
Newer releases are sent first to those members who have had the game in their GameQ the longest. (First come, first serve.) You need to add upcoming titles to your queue as far in advance as possible, weeks to months before they are released. That will improve your odds of getting the title on or near release day tremendously.
Newer games that are in high demand will always take a while to ship out unless you added that game to your queue a long time in advance.