The Karamazov Brothers is, quite simply, Dostoyevsky's greatest work. The characters are superb creations, the settings stunning and the pace is breathtaking. The book itself is a discourse on religion, existentialism, innocence and rationalism, and comes to some absolutely mindblowing conclusions. The chapter entitled 'The Grand Inquisitor' is the pinnacle of Dostoyevsky's career, beautifully constructed, stunningly written and with fantastic ideas.
The Karamazov Brothers is a difficult work, and it helps if you've read some of his other works before starting, particularly the Idiot and the Posessed/the Devils. This new translation is one of the best of its kind, and well worth buying over other editions. A helpful introduction, chronology and character list make this a great buy.