I disagree with all the above
You just have to know in wich disorder you can read them.
For instance after reading book 1, you can perfectly read Midnight Tides, since it is also somwhat of a beginning but in another end. Or after book 1 you can also read Memories of ice.
That said, for the third book, it is definitly better to have read the second one first. As for the last two, these should best be read after you read all the others, cause those two dont stand so well as read/stand alone books.