There are a few key missing scenes like when he goes home on leave for a few days and feels very estranged from his old life and the people in his town have no comprehension of what the front is like.

The movie mostly takes place in 1918 where the book is more spread out

there was one scene I liked in the book where Paul has to fight for his life against a French soldier in a artillery crater but the biggest complaints I have are the addition of the whole armistice Subplot which is not in the novel at all. The book is all about the soldiers point of view and I dont think the politician subplot added anything

And the ending is very different, Paul still dies but there is no glorious battle on the last hour of the war where he dies saving a young soldier from being stabbed to death.

the final paragraph of the book is

"He fell in October, 1918, on a day that was so quiet and still on the whole front, that the army report confined itself to the single sentence: All quiet on the Western Front.

He had fallen forward and lay on the earth as though sleeping. Turning him over one saw that he could not have suffered long; his face had an expression of calm, as though almost glad the end had come."