The ending of this novel is rather sudden. Let us remember that it is when Onegin asks Tatyana to be his mistress, having rejected her advances two years before, and Tatyana admits to him that she still loves him, but that she will remain truthful to the vows of marriage she made to her husband, whom she married in Onegin's absence after he rejected her. At the point, the narrative suddenly stops with Onegin facing Tatyana's husband:

She went -- and Eugene, all emotion,
stood thunder-struck. In what wild round
of tempests, in what raging ocean
his heart was plunged! A sudden sound,
the clink of rowels, met his hearing;
Tatyana's husband, now appearing...
But from the hero of my tale,
just at this crisis of his gale,
reader, we must be separating,
for long... for evermore.

The sudden intrustion of the narrator and the way that he ends the tale so abruptly serves to greatly heighten our interest in what happens next to both of these characters and the various futures that they face. The narrator seems to delight in this "abrupt ending" as he calls it, as he knows he is leaving so many questions unanswered, and in a way he is deliberately doing it to give his audience so much to think about and debate. Will Tatyana remain truthful to her vows? Will Onegin find another love? The abrupt ending serves to heighten our interest in the novel by making us think through such issues and giving us the chance to predict the fate of these characters.