The first (of four) parts--Prince Myshkin's arrival home; his meeting with the Epanchins and the Ivolgins and the great culminating showdown with Nastasia--that has to be among the best things that D ever wrote. The trouble is, he doesn't quite know what to do for afters: he's got 440 pages (out of 615) still to go and he simply wasn't able to find a way to fill the remainder with the same kind of focus and energy. To make it work at all, he has to do a couple of things you wouldn't want to do in a novel: one, he virtually has to reengineer not only his protagonist but several other of the main characters--endow them with personalities and motivations perhaps interesting enough in themselves, but discontinuous with what you saw in the first part. And Nastasya, his most interesting character after the prince himself--her big scene is so hard to top that he more or less drops her, turns her into a shadowy offstage presence until near the latter end of the book.
But wait, don't leave yet--even with this (what shall we say?) failure of nerve, there's a great deal in the book to reward one's continued attention. There are half a dozen scenes which, if not quite up to the splendid opening, are still way ahead of what almost any other novelist could concoct, then or now.
I think you can call it "personal" to D in at least two respects: one it is the novel where we find material that most closely tracks D's own life (including a harrowing "mock execution" that must be a record of D's own first-hand experience). And two, it is the novel where D first grapples at length with the religious themes that come to dominate his thinking in Brothers, still a few years away. By corollary, I suppose this shows why some readers make it a personal favorite of their own: you make contact with D himself and his most urgent concerns in a way that not even the Brothers can equal. Frank may justly be given the last word:
With an integrity that cannot be too highly praised, Dostoevsky thus fearlessly submits his own most hallowed convictions to the same test that he had used for those of the Nihilists--the test of wht they would mean for human life if taken seriously and literally, and lived out to their full extent as guides to conduct. With exemplary honesty, he portrays the moral extremism of his own eschatological ideal, incarnated in the Prince, as being equally incompatible with the normal demands of ordinary social life, and constituting just as much off a disruptive scandal as the appearance of Christ himself among the complacently respectable Pharisees.Joseph Frank, Dostoevsky: A Writer in His Time, Ch 40 (2010)