Hi there,
There is no shortage of nice hotels in Siem Reap but I would advise you to book ahead nontheless. Whatever you do, be sure to fly from Bangkok to Siem Reap, the overland border crossing is traumatic! While Siem Reap is a nice place to spend a couple of days, Temples of Angkor, floating village, nice bars and restaurants, Phnomh Penh is a different story. It is worthwhile seeing S21 and the Killing Fields but then leave as it is not the type of city you would stroll around. About 4 hours by bus south west is Sihanoukville, a fab beach.
We found Cambodia hard work to be honest, poverty everywhere, people begging and ripping you off at every corner... it wouldn't be my ideal honeymoon destination... one time we had breakfast on the beach and there were four people sitting beside us waiting for our leftovers. The country has never really recovered from the atrocities of the Khymer Rouge regime.