There's one scene, in particular, where Jacob is crying, forced to relive the death of his son that's like a punch in the gut, mostly because it's a Foregone Conclusion. Tim Robbins does an incredible job of portraying the feelings of grief and anguish that his character feels.
The one moment happy moment Jacob has, with his ex-wife and kids in a hospital, a disembodied voice mocks, "Dream on".
The end of the movie when Jacob returns home, accepts that he is dying and is reunited with his dead son, who guides him up the stairs toward Heaven, represented by a bright golden light.
The entire movie, boiled down, is about a man who hasn't reconciled the death of his son, who was killed while he was away in Vietnam, and struggles the entire film to deal with it.
In the final Deleted Scene when Jacob discovers Jezzie was himself. The sad expression on the face of the doppelganger just sells it.