Can you tell us a little bit about why it's so good? This is obviously one of those legendary books I've heard a lot about, but I don't know anything about it. What's good about it?
Sure !
Well other than the fact that the writing is godlike, I think that the greatest aspect of the book is that it makes your brain work way more than most books without you even realizing it. I mean, when you look at it, the story is very simple : a student, named Raskolnikov, commits murder and then feels guilty (hence the title of the book). That is how the book is usually summed up and it's pretty accurate story-wise.
But the story, even if very interesting, is almost a "pretext" for Dostoyevsky, to describe his whole world and expose his idea. The story is essentially about what causes crimes to happen (is it poverty ? Is it just human nature ?), and the concepts of remorse and redemption (should we feel guilty if we kill someone ? After all, many great men in history are responsible for millions of death..). Throughout the book you'll constantly be asking yourself questions, and will probably be rooting for Raskolnikov (meaning not wanting him to get caught or turn himself to the police), which is quite disturbing because well, he's just a killer, there's nothing great or remarkable about him..
So yeah, to answer your question, I think that the reason it's so great is that it remains interesting to read (in the sense "damn I wonder what happens in the next chapter ?!") while being one of these few books that really make people "smarter" and make us realize that there is a lot to consider when talking about crimes and the way our societies should investigate/punish it.
Plus, the edition I read was divided in parts of 150/200 pages and it was a very good way to read it, by reading one part a day you'll have finished it in les than a week so I can only encourage you to read it !
P.S : Do not hesitate to tell me if something in my message is unclear, English not being my native language I'm not exactly sure of how clear I am..