There's quite a lot to say on the subject and I'm not quite ready yet. In case you'd like a preview, though, you could take a look at this page of thumbnails which covers all the sides containing a miniature.
Compare those to a typical text page (f. 166r) in order to appreciate the artistry of the miniaturists.
One of the things I've learned in the last week is that, in addition to the standard contents, the Belles Heures of Jean de Berry also includes seven “picture book” cycles that tell stories through a set full-page illuminations. On these pages the text is limited to a few lines in alternating red and blue ink. The brief texts included on the pages are not devotional, like the texts in a typical book of hours, but rather relate stories from the lives of the saints.Different pages have different-sized miniatures. There are two main sizes:
More rarely, a page might come in one of these two forms:
One-quarter page illustrations, e.g., Angel Destroys David's Enemies (f. 66r); St. Michael the Archangel (f. 158r); St. Benedict (f. 175r).
Full-page miniatures, e.g, Annunciation to the Shepherds (f. 52r); Descent from the Cross (f. 80r); Pentecost (f. 84r); Heavenly Host (f. 218r); The Duke on a Journey (f. 223v).
Two one-quarter page illustrations, e.g, Trinity and Duchess at prayer (f. 91v); Pentecost and the Trinity (f. 155r);
One-half page illustrations, e.g, Duc de Berry at prayer (f. 91r).