Cool breeze, good food and friendly Khmers
Yeah, the Riverfront is Phnom Penh's major attraction, esp. on Sundays when scores of Cambodians come out to stroll along the Riverfront, have a picnic in the park in front of the Royal Palace, play games with their kids and have their pictures taken by some 'professional' photographer. A great atmosphere.
When getting thirsty, have a drink at the FCC. From their balcony, the view on the crowds below and the confluence of Tonle Sap and Mekong is great. Food is on the expensive side though. Better option is frizz cafe restaurant, for a taste of genuine Khmer food, yummie! They are just past the 'happy' pizza places.
The Riverfront dies down early, around 11 at night. But, no need to go some other part of town. Just one block from the Riverfront is the Ginger Monkey Bar, with a delightful atmosphere. They organize special theme nights regularly.
So, yeah, enjoy a day on Sisowath Quay!
(official name of the Riverfront)