Joaquin Navarro-Valis said (at the vigil before the feast of Divine Mercy) that if we are to understand Pope John Paul II "one must first understand Divine Mercy".
It is rare for a private revelation to receive such public acclaim. Pope John Paul also showed his approval for the Marian Movement of Priests, especially by personally inviting Don Gobbi to celebrate his 25th anniversary of ordination with the Pope in his chapel. There are stories of him expressing positive comments about other mystical events. It is best not to mention some of them, however, because these things are often vociferously refuted and denied. There is no doubt about MMP and Fr. Gobbi nor about the Popes's acceptance of the writings of St. Faustina.
As I have said in a previous post, mystical experiences and revelations are part of the Church's history, going right back (at least) to St. Paul and his experience on the road to Damascus. As is well known, Pope Puis XII accepted Fatima (although, initially, in a limited form). He even based one of his encyclicals on it (Signum Magnum). Pope Paul VI also accepted Fatima and gave the shrine a Golden Rose which is a sign of papal approval. When Pope John Paul the FIRST arrived on the scene one of the first things he did was to welcome the pilgrim statue of Our Lady of Fatima to the Vatican. There are many who dislike mystical events - perhaps because these things are beyond their control, whether intellectually or emotionally, and perhaps because they seem to bring God even closer to our daily lives (and some people like to keep God in His place!)
So much has been given to the Church and the world through mystical experiences and private revelations (e.g. St. Margaret Mary's apparitions and the message of reparation etc). Of course we need always to be careful and, of course, such things cannot be regarded as important as the Holy Scriptures and Tradition. Nevertheless, when Heaven gives these gifts we must be careful not to be too dismissive. In this regard St. John of the Cross is often mentioned as though in support of a dismissive attitude, but that is to misunderstand his background and to have a poor grasp of his teachings. With St. John of the Cross it is important to remember St. Teresa of Avila!