I visited this WHS in September 2012. It is truly a hidden gem! The terracotta monuments are a treasure chest of mosaics, one more beautiful than the other. I visited all 8 listed sites and my favourite is the Cappella S. Andrea (Arcivescovile), a small private chapel with fine mosaics (the highlight is the gold/blue sky with 99 species of birds). The least aweinspiring of the sites was perhaps the Mausoleo of Teodorico which is quite a walk out of the historical city centre. The Basilica in Classe is also worth visiting. I reckon Ravenna is one of my favourite WHS in Italy.