While Siem Reap is a small provincial town with rural sensibilities, Phnom Penh is very much a big city. It's crowded and the people aren't as friendly. The girls often dress with a sense of fashion and there's plenty of flash cars to prove that some Cambodians are wealthy.
Cambodia has a reputation as a very corrupt country. We we're never directly affected by corruption but we heard lots of stories. For example, the terrible road between Siem Reap and the Thai boarder never gets fixed because its alleged that Thai Airways pays a bribe to keep it that way. The guides we had technically work for the government but they give their salaries to their boss in exchange for not showing up at work. Instead, they all freelance and earn more however, they will still get a pension one day.
The roads in Phnom Penh are still dominiated by swarms of motoscooters. There's little sense of road safety and there's even less sense that there are any rules of the road. Many cars don't even have licenses and I heard many license are fake. Few helmets are used. Our tuk tuk didn't even use lights at night. At intersections, there's often no traffic lights or stop signs. Everyone just goes and weaves around each other! The main rule is that smaller vehicles make way for bigger vehicles and there's safety in numbers. Crazy.
Our first day, we visited the Tuol Sleng prison (S21) and the Choeung Ek Genocide Center at the Killing Fields. I've spent some time trying to understand Cambodian history since independence but its been a struggle to understand the Khmer Rouge and the purpose behind their brutal policies. The portraits of all the children they put to death at S21 was really upsetting. What I can't reconcile is this nice country and people with such a horrific past.
We also visited the Royal Palace which was fine but not overimpressive. It lacks the finish of fine artisans. We spent quite a bit of time at the Water Festival down by the riverfront watching the boat races. The tourist board had a special pavillion for any tourists which made it very easy to get a good view. The crowds in the city were phenomenal.
Unless, you are interested in the Khymer Rouge history, I don't think its worth visiting Phnom Penh. Rural Cambodia is more interesting than its cities.
My enjoyment of the trip was then cut short. I came down with a high fever and spent three days lying in my hotel bed while the family continued sightseeing. At least the Sunway Hotel was a very nice place. My fever broke just in time for us to fly to Bangkok. It seems it was a nasty flu.