The fact that Jackson didn't give us Gandalf's confrontation with the Witch King at the gates of Minas Tirith is so ridiculous. It's decisions like this that has lowered my opinion of RotK, over the last 20 years.
One of the most epic moments in the entire book, and Jackson completely rewrites the siege. I honestly don't understand the point of this change. It reeks of the Halfblood Prince movie changes, adding the Burrow scene. I'm stuck asking, "Why?"
The sheer imagery of a scene like that would have been beautiful to see. Instead, we get a stupid extended edition scene where the Witch King destroys Gandalf's staff. What? Are you serious? Where the hell did that come from? I truly hate that scene and just wish Jackson had more faithfully adapted the siege of Minas Tirith.
This also leads to another weak point of the Siege of Minas Tirith... a lack of characters. We never really get to know Minas Tirith or its people, in the movies. I think it's one of the reasons the stakes don't feel as high as they do in the Battle for Helm's deep. In the book, we get so many great scenes with Beregond and Pippin, which does so much to make us care more about the people of the city. Also, there are SO many more heroes in the books I wish we got to see kick ass. No Prince Imrahil and his knights, no Dunedain (including Halbarad), no Sons of Elrond, and no other lords of Gondor.
I was okay with Eomer not being at the Battle of the Hornburg because we do get one of the most epic moments in the entire series, with him leading the Riders to rescue the King. But I just wish we got more for the Siege of Gondor and Battle of the Pelennor.
I kind of get what Jackson was going for. He was building a world where the men of the west have basically fallen into uselessness and despair, with not much fight left in them until our heroes appear to save the day. In the books, it wasn't like this. The men of the west were still strong and proud, but were disjointed because there was no King to truly unite the free peoples under one banner.