I agree with the Ent comments. Moreover, Jackson made the Ents downright hasty. He sees the tree stumps (which he somehow didn't know about, even though the trees all talk to each other throughout the forest) and immediately gets all hot, and suddenly there's all these Ents right there with him and all of them immediately are called to action...
The march of the Ents is one of my favorite passages from the books, so to leave it out as well as completely subverting the nature of the Ents was a huge disappointment to me. The storming itself was great, though
I consider myself a Tolkien scholar, having read biographies, literary criticisms, Tolkien's drafts, and so forth so I take the books pretty seriously. Of course I had lots of minor beefs with the movies. But there were very few that actually made me like the movies less. The betrayal of Fangorn's and Faramir's characters were two of those. I'm glad that the EE made Two Towers bearable for me (I loved FOTR and ROTK, though).