The collection is quite small for a national museum. Most of it seems to be from the Angkorian era, even the temples of Angkor, and includes Hindu statuary as well as Buddhas.
There are some Champa phalluses, two monkeys wrestling, and some other stuff. If you read every bit of signage, you would still be out of here within an hour.
While the Museum butts up against the Royal Palace, it's another fifteen minute walk around to the entrance. The palace is closed for lunch, but don't believe tuk-tuk drivers who tell you it's closed for the day and offer to take you for a ride--they're trying to take you for a ride.
Above is the exterior of the King's ceremonial meeting hall, Preah Tineang Tevea Vinichhay. The king is Norodom Sihamoni, son of Sihanouk. The main draw of the place, though, is probably the Emerald Buddha temple, which is much like the one in Bangkok.
Also like Bangkok's palace, this one has an outer wall decorated with murals purporting to tell the history of Cambodia. Of course, they don't really, since at no point did monkey gods ride golden carriages and lead troops into battle.
The three photos above show pretty much the best images I saw. In other words, these frescoes are in appalling condition, even though the building only dates from the 1800s. This was sad, because clearly they were once very beautiful. Today, they suffer the humiliation of being used for lumber storage.
The entrance fee for each facility was around USD 5 or 20,000 riel, as was the case at most sites I went to. I should mention that you don't need to exchange dollars for riel, as the greenback is accepted as currency literally everywhere in the country.