The carving on Banteay Srei, and the pink color of the limestone, is absolutely beautiful. Though you may be tempted to skip it, I'd say it's worth a journey. You may find the 30+ minutes relaxing, though perhaps not.

Angkor Wat itself is overwhelming. Obviously, it won't be missed by anyone visiting. It's so overwhelming, in fact, that one might easily miss some of the details and finer beauty it has. One temple on most itineraries that, I would submit, should be on everyone's list is Angkor Tom: the grey stone temple with scores of enigmatic Buddha faces peering out from its surfaces. That was amazing.