Yes, White Nights is one of the best doorways into Dostoevsky: it is short, has only two characters on stage for most of the time and a story that is easy to follow, told over four nights and one morning. At the same time, it already carries what the author will develop later: the lonely man of St. Petersburg, the long confession and the question without an answer at the end.
It has clear advantages for those beginning. It came out in 1848, in a magazine, months before Dostoevsky's arrest, and it is a work of youth, with the tender tone and the humour of a narrator who laughs at himself. There are few Russian names to remember: the Dreamer has no name, Nastenka is Nastenka from beginning to end, and the lodger and the grandmother are called only that. The plot is linear, and the meetings repeat in the same place, the bench on the embankment.
It is also necessary to know what it is not. It does not have the police plot of Crime and Punishment nor the great debates of ideas of the mature novels. The long discourse of the Dreamer on the Second Night, in which he speaks of himself in the third person, asks for patience, and the book resolves nothing: it ends with a question. Whoever expects action may find it slight; whoever enjoys character and voice finds it rich.
A good reading order is to start with it and then move on to Notes from Underground, of 1864, where another man of St. Petersburg who lives in a corner reappears, now without the tenderness of this narrator. Some readers prefer to begin with the great novels and leave White Nights for later, as a rest; the book works either way.