If you're into mysticism, you're absolutely going to love St. Catherine's dialogues. A couple caviats to differentiate this from the rest of the spiritual classics. This shouldn't be your first pick when you're sizing it up against works from de Sales, de Montfort, Lisieux, St. Faustina, etc. I would absolutely liken the writing to St. Teresa of Avila in terms of how long and complex the sentences and thoughts are. You really have to be dialed in, but if you are, you've absolutely found treasure for yourself.
Another important distinction is that it's a dialogue with God the Father, which gives a slightly different but exciting perspective on the world compared to Jesus or the Blessed Virgin.