Ok yeah, you all know what and where Diamond Island is but how often do you actually go out there? I am the same, not often, but every time I do I make a mental note to do so more often, it is a multi faceted place, and it is very Khmer in so many ways.
I sometimes travel out there very early in the morning and just stand and look at the confluence of the Mekong and the Bassac rivers, I watch the ferries going back and forth to Silk Island and stare and wonder when the Sokha Hotel will start to make money, maybe when riverside eventually expands all the way out there, if it does they will have a goldmine of course.
The promenade along the front, while not too long, is very pleasant with groups all ages just hanging out, taking selfies or maybe buying a padlock for thier songsar, or the one they wish to marry.
Then if you want to go really local there are regular concerts and events which attract a massive local crowd, and then the big restaurants, these huge suki places are some of the few eateries in Phnom Penh which must be making money hand over fist, they get so busy!