Angkor Wat's just one temple, admittedly the most immediately impressive. There are plenty of other temples/sites to see at Angkor.
Plus there's a boat tour on Tonle Sap with the Vietnamese floating villages, a crocodile farm, modern Buddhist temples, drinking, eating, shopping and massages. Though the massages are a bit crap in the cheaper places and tourist tat is tourist tat. But you could spend 5 days just in Siem Reap and not get bored. Personally I think 5 days is too little time to go to more than one place. Perhaps you have more energy than I do?