I've seen people writing and questioning Zeus' actions, saying they don't make sense as he is helping Hades out, and then turning around and helping Perceus. He also doesn't seem particularly upset that the plan to punish man failed, and that someone who stood for "Man over the Gods" was the hero of the day. Doesn't make sense, does it?
Honestly, my answer is yes. Simply put, and the best way to understand this is what does Zeus lose in this movie? Nothing, nothing at all. Do you really think that when the story gets out that Perseus the son of Zeus defeated the Kracken and saved Argos that the reaction from the people isn't going to be that Zeus planned it out, that Zeus sent someone to save them? So, either way this thing plays out, Zeus wins really. Either Hades does his thing, the people get punished and turn to the gods for help (something we are shown is already taking affect when we see a soldier asking forgiveness and praying to Zeus), or his son saves the day at which point it is "Thank the gods! They sent a hero to save us!"
Zeus, from how the movie shows it, does a rather good job of playing both sides. To the other gods, he seems to be ready to punish man kind. They are there when he sets Hades loose on man, a far different action than what he did last time a man defied the gods. On the other, he is instrumental in helping Perseus on his journey and saving man kind. He wields both the carrot and the stick. However, that isn't the Xanatos Gambit I'm talking about, though it is an instrumental part of it.
A Xanatos Gambit depends on using the opponents moment of victory to attain your own. So, in the movie the gambit is actually being done against Hades, as it is Hades moment of victory that leads to Zeus' greater victory. Zeus hides his love for his son, going so far as to say that Perseus is the same as the other humans because he does not pray to his father when told of Perseus' presence in Argos. Zeus secretly helps Perseus along the way though, giving the sword, the coin, and the pegasus to help along the way.
Meanwhile, Hades being given permission to go forward launches his plan to punish the humans, gain power, and take over Olympus. For this end, he needs Zeus to allow him to unleash the Kracken, something he does get. With power coming to him, he makes his move, only for Zeus to warn him that there is a demi god in Argos.
Now, what threat does this have to Hades plan if not for the possibility of Zeus winning this way? Hades understands that his own moment of victory (the Kracken being released) is the key to Zeus getting his way. The people will praise the gods as they are saved from the very real threat they saw with their own eyes by Zeus' son. This love and praise, directly primarily to Zeus for sending his son, would turn the tides before Hades could win fully.
Now, I'm not saying the movie is great, and the plot is simple, but if you are looking for a fairly clear cut example of how a Xanatos Gambit can work, and how a person can play both sides giving themselves a win/win (or possibly even win/win/win) situation. You can do worse than looking to this movie. Especially since you get to see the Gambit play out from a side that it is not being played against, meaning you get to see more of it.
So keep it in mind, happy gaming!