The Epilogue, Why People Dislike It
When I first read this book at a teenager, I agreed with a lot of critics that the epilogue was tacked on, and did not do justice to the intensity of Raskolnikov in the rest of the novel.
I thought perhaps it was Dostoevsky's attempt to add on a Christian ending, though the real truth of the novel was otherwise.
When I re-read it recently, my opinion was absolutely changed, and it struck me that maybe it is that the people who dislike the ending are those that basically share Raskolnikov's original philosophy.
Not that they condone murder, or are anywhere as extreme as Raskolnikov was, but that they basically have a materialist, utilitarian philosophy where the end justifies the means, that there is really not an innate value in every life, that reason, and ideology based on reason, trumps all.
I now see the epilogue as an organic part of the novel. The novel ended in a kind of intense cresendo, and in the aftermath Raskolnikov seems angry, perhaps beginning to renege on the renunciation of his former philosophy, until he has his dream of the virus, and the subsequent realization of Sonia as a way out of the mess his former ideology entailed.
This is how changes in outlook often happen, I think. We don't often logically re-assess our belief structures and sort everything out methodically. Rather, something from the subconscious shifts, as in Raskolnikov's dream and moment after seeing Sonya at the prision gates, and everything reorders on its own.
In defense of those who didn't like it...
I would find it a lot easier to say it wasn't just Dostoevsky plugging Christianity if he didn't plug it in so many other books that he wrote, in similar ways (ie. an answer to philosophical questions which the non-Christian characters, given whatever talents they have and have not, can't find anywhere else), and if he didn't write so extensively about the not-yet-understood importance of the Russian Christ to the rest of the world (though the world would understand this when Russia "revealed it to her," which was, according to him, Russia's highest purpose and goal) as well as Panslavism and Jews being the scourge of the Earth, in his Diary of a Writer, as well as in many of his articles for Pravda themselves. Christ was a philosophical as well as a spiritual solution.
Not to say that it wasn't ALSO bad/good/whatever it was because he wrote it quickly to pay off debts.