Did Jackson Make the Right Call With This Major Change to LotR Canon?
One big change to The Lord of the Rings canon which Peter Jackson's movie trilogy made was making Saruman appear to be a minion of Sauron.
While in the book Saruman's sellspeech to Gandalf similarly stressed the impossibility of prevailing against Sauron and the need to join the winning team, and Saruman maintained an appearance of alliance with Sauron, subsequent events made it amply clear that Saruman's true plan was always to seize the One Ring for himself.
And that made him a mortal enemy of Sauron, only cooperating with Sauron temporarily for his own gain, and intending from the beginning to betray his new master as well.
Indeed, the book explicitly pointed out that Saruman saw himself as a rival of Sauron, while in truth he was only a pale imitator, and everything he did after turning to evil was only miniature copies and cheap knock-offs of the Dark Lord's wicked but grand designs.
In the movies, however, this aspect is significantly toned down. The fact that Sauron still commanded his Uruk-Hai to bring the hobbits (and, consequently, the Ring) to Isengard is never emphasized, the hostility and suspicion between Sauron's and Saruman's orc servants is removed entirely, and the scene of Saruman explicitly taking orders from Sauron through the Palantir is added.
This undermines the narrative's logic.
In the book finding the Ring is all-important to both Saruman and Sauron, they constantly attempt to figure out the Ring's current location, launch their military campaigns based on their guesses, and their rivalry is a large part of the reason why they fail, with Saruman's servants dragging the captured hobbits in the opposite direction from Mordor, and so on.
In the movies past the first one they seem to lose their interest in it.
On the other hand, the movies were already somewhat overloaded with information for any viewer who did not read the book. Some simplification might be considered justified in the light of this.
The book could easily devote a few paragraphs worth of descriptive text or guesses by Gandalf to briefly outlining what the bad guys were thinking. The movies had to work with much tighter restrictions. Turning Saruman into little more than Sauron's underling on the first glance, while retaining enough ambiguity about it through not explaining the details, might have been the right choice.