The Merode altarpiece, despite its large significance for Western painting, as explained by JMS, is a cramped and cramping allegory. So, the mousetrap--worked on by Joseph--represents Christ, God's bait for the devil (a metaphor from Augustine), the lilies represent the Virgin's purity, the sixteen sides of the table represent the sixteen major prophets of the Bible, so on and on. But I am no longer moved by such dry correspondences.
The smallness of the books, of the ivory and wood carvings, adds to my feeling of a dark, confined space. The detail is spectacular, and the line, as in a tiny torso of an armless Christ on the cross, is sometimes sensuous and sensitive, but the devotional objects demand a narrowing of the eyes, and not an expansion of vision. The stuff I like best, like the Standing Virgin and Child (ca. 1470, attributed to Nikolaus Gerhaert von Leiden) are usually late in the period, closer to the Renaissance than the Middle Ages.