Agreed, they couldn't have really done the Scouring of the Shire scene, so I wouldn't be upset about that if i were you. It wouldn't have felt like the movie was just never ending at that point. the main story was wrapped.
Plus you got a little taste of it with the flashforwards they showed in the mirror of Lothlorien.
You have to remember that it isn't the movies job to verbatum copy the book. There are certain things that don't work in every medium, so it's more than understandable that they left this out, it was necessary.
I don't know what other important things they left out. Bambadil again is useless to the main plot. Maybe there were a couple little other things, but the movie itself was near perfection for what they needed to accomplish.
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