Some of the changes I can understand from a theatrical point of view. As awesome as he was, Tom Bombadil did nothing for the story, other than taking the Old Forest arguably makes more sense than taking the road. Glorfindel was in it for just the one scene, so it was easier to conflate him with Arwen. And even if you don’t like the change, can you at least agree that the Oathbreakers swarming the oliphants was pretty awesome?
Changes I didn’t like, however, included Faramir and Aragorn, Narsil, and the scouring of the Shire. Faramir wasn’t swayed by the Ring nearly as much as his brother was, but they were both weak in the movies. Aragorn is supposed to have wanted to be king this whole time. Narsil should have been with Aragorn, partly because one of my favorite scenes is at the Prancing Pony. The part where he stands over the hobbits and places his hand on Narsil’s hilt as if he was going to draw it (but doesn’t because a broken sword’s not so menacing). Finally, the scouring of the Shire is actually fairly plot important, and Jackson probably could have moved the Palantír into Two Towers to make room