The most drastic changes in the film come at the expense of the gods. Many watching the movie wonder why Danny Huston would have been hired to play Poseidon when he has almost absolutely nothing to do in the film; the answer is that nearly two thirds of the business with the gods was edited out of the film, and the very tenor of the god scenes was changed in fundamental ways.
In the original version of Clash, Zeus is the bad guy. He's a god who has sort of lost it, and it's unmistakably his fault that the humans have turned against the Olympians. The rest of the gods play a significant role in events, especially Apollo and Athena, who barely appear in the theatrical cut of the film. The younger generation of gods are afraid, realizing that Zeus' mismanagement has led them to a serious crossroads in their history, and that if they don't take action, they'll lose all their power.
Meanwhile, the very nature of Perseus' quest is quite different in the original version. As I mentioned in my review, my visit to the set of the film had revealed that Gemma Arterton considered the relationship between her character Io and Perseus as a brother/sister one; the finished film isn't quite so fraternal, with the two having a romantic connection. But Arterton was speaking before the reshoots that redefined the relationship.
In the original version Perseus was in fact romantically drawn to Andromeda, giving Alexa Davalos much more to do. But there was more to it all than that; while falling for Andromeda gave Perseus a better reason to go questing in the first cut (as you'll recall the finished film has him hitting the road only to get vengeance on Hades, a concept that was added in reshoots), it also gave the script a chance to lay out some of the film's basic thematic points. Perseus felt that it was important to save Andromeda not just because of how he felt about her but because he believed no humans should be sacrificed to placate the gods. To Perseus the quest was not just to save the woman he loved but was also a way to prove a fundamental belief - that humans were just as, if not more, important than the gods. To Perseus sacrificing anyone to the gods was the act of a subservient people who were in bondage, and that humans should break free of that bondage. There are elements of this secular humanist viewpoint in the finished film, but this was a much bigger, more important aspect in the original.
There's more. In the film Zeus has a mysterious and unexplainable change of heart about Perseus, his bastard son. While Perseus is on a quest to destroy the gods Zeus shows up and helps him out, which doesn't quite make sense. In the original script (and the original cut) it wasn't Zeus who showed up to give Perseus the coin he needed to cross the River Styx - it was Apollo. Apollo, Perseus' half-brother, takes it upon himself to help the demigod out because he understands that Hades is playing Zeus and that all of the Olympians are heading for a big fall. The god of the underworld would be happy to see the rest of the pantheon destroyed. Apollo and Athena essentially betray the other Olympians to give a boost to Perseus, thinking that he could be the one to shake things up enough to allow a change in Olympus. There's a layer of palace intrigue here, with the gods planning and plotting against each other. The exclusion of all of this meant that the coin scene needed to be reshot, with Zeus getting most of Apollo's dialog; more than that it meant that much of the layered, almost Claudian drama in the script was completely discarded.
These changes are, technically, minor - but they add up in a big way. The theatrical cut of the movie repositions Zeus from a more villainous character to a bumbling but sympathetic distant dad. Yeah, maybe he raped Perseus' mom, but he's not that bad a guy, and he's there for his son in the end. By making some judicious cuts and reshooting only a few scenes, the current cut of Clash betrays the spirit of the shooting script.
All of those changes to theme and to the central concept of the gods necessitated a change in the ending. The final scene of the theatrical cut is, frankly, disastrous - not only is Perseus suddenly best buddies with Zeus, but Io, who had previously called eternal life a curse, is resurrected in what we're supposed to accept as a happy ending. None of this could be farther from the ending of the original script and, presumably, Leterrier's first cut of the film.
To start off - there's no defeat of Hades in the original script. While Hades is a villainous story motivator, he's not the Big Bad of the tale, so Perseus is only dealing with the Kraken in the finale. Perseus' victory, along with Apollo and Athena's help, reveals Hades as a manipulator and the gods are able to crack down on him. This is a huge improvement simply because Perseus casting Hades back to the underworld is so unsatisfying in the theatrical cut; it's not a real victory of any sort, since Perseus' quest in the film was to kill Hades and he doesn't really do that.
Beyond that, Perseus goes to Olympus at the end of the original script. Zeus thinks that Perseus has come to finally take his place in the pantheon, but the reality is that Perseus throws the magic sword at Zeus' feet and tells the god that while he may be Perseus' genetic father, his real father is a dead fisherman. All throughout the original version of the film Io had been warning Perseus that the gods would corrupt him by offering him everything he ever wanted; in the finished film our hero is corrupted by Zeus, but in the original version Perseus remains his own man. He puts Zeus on notice.
There are other, smaller changes from the shooting script, many of which flesh out the group who travel with Perseus on his quest. The original script reads more like a men on a mission movie, with each character having their own moments. There's a terrible logic in these scenes being cut for story economy, but the rest of the changes baffle. Some make the movie internally inconsistent, while many others rob the film of its thematic resonance and meaning. Changing Perseus' motivation, softening the edges of Zeus, cutting the other gods from the story (including completely chopping Athena, who has two major scenes in the original script), and screwing with the ending all add up to a film that doesn't quite work and that feels tinkered with. I don't think it takes insider knowledge to watch Clash of the Titans and see that it's covered in fingerprints.
But whose fingerprints? It's hard to say from this vantage point. I haven't seen the original cut that Leterrier delivered, so I don't know why the Andromeda/Perseus love story was excised in favor of a Perseus/Io love story, although I suspect it's because Io is more present throughout the story. My suspicion is that the changes were made in an effort to give the film a broader playability - and to some extent the box office numbers prove that the changes certainly didn't hurt the movie's business.
What now? Some script changes were made on set, so some scenes never got shot, but there is a ton of footage of the gods that exists. Could there be a director's cut of the movie one day released? There are two major obstacles to that at the moment: first of all, all of the god scenes presumably need FX work (all of the Olympus scenes have a processed, fantastical look, and the floor of Olympus is a very cool birds-eye view of Greece, which I'm assuming is CGI). But more sticky is the fact that this cut would be a movie that has a completely different throughline and ending. With Clash performing as it is it's not unlikely that a sequel could be greenlit, so would Warner Bros want to put out a version of the movie that completely contradicts whatever will come next for the franchise?
I wish they would. There's stuff in Clash of the Titans that works - lots of fun moments and action set pieces that thrill. But there are other things that simply don't. The shooting script presents an intriguing alternate version of the film, one with more humor and characterization and one with much more intriguing philosophical stakes. The ending of the original sets up fascinating avenues for a sequel, and feels like the beginning of the next step in Perseus' journey to free humanity from the yoke of godly oppression. Instead we ended up with a movie where our hero sells out to the man.
