Cambodia is a wonderful place if you look for adventures, great locals markets and a warm and polite population, that is normally always happy to give you a hint or an advice.
Few personal insights:
1) Bus service works great in the country, while train might not be the best solution (however if you are a little bit persistent you might be able to try the adventure of traveling on a cargo train)
2) Less touristic than Thailand, which means also less expensive.
3) There are various cooking lessons of Khmer food around the country if you are a cooking lover
4) Amazing little paradise for BP situated in the south coast, called Sihanouksville. If you run out of money you can stop there and easily found a job as a waiter etc.
5) Be careful in crossing the border from Thailand to Cambodia. Some cities on the border are a little bit dangerous and it can be a problem to find a "real bus", cross during the day.
Country overview by
Facts about Cambodia
Stuff to See and Do
Where to Stay
Finding A Place To Stay
When I was in Cambodia, I learnt that you don't have to take the first place you get to. Walk around and compare until you are happy with what you choose.
It's for this reason that I love backpackers and hostels because there are so many at your disposal so you end up with the one that suits your personality, and that is what is important.