I just got back from Cambodia over Christmas. We spent the majority of the time in Thailand and 2-3 days in Siem Reap to check out Angor Wat. We spent 2 almost full days at the Wat but wish we could have spent more. It is very draining though, and ideally I would take a day off in between. Its really hot, so around 1pm you are spent after being in the sun all day. Going to the We didn't have too much time to do anything other than the Wat. If we did have more time I would have done the trip to Battambaug and the boat down the river to Phnom Penh. We ended up taking the overnight bus which was awesome and much cheaper than flying. I don't trust the Cambodian airlines that fly between Siem Reap and Phnom Penh. Safety record and they wanted us to pay through paypal. Apparently they are owned by a casino and pilots pay to fly the planes. Yikes!
We spent maybe 16 hours in Phnom Penh and liked it. But not sure what else was around.
Lodging was really cheap in Cambodia. $10-$15 a night for a guesthouse (small hotel with maybe 15-20 rooms) with a pool. Food was a little cheaper than American prices but not really too much. For the wat, plan to spend $15 a day for a private tuk tuk to drive you around. I know lots of places say the best way to see the wat is on bike. But it was way too hot and humid and the places to rent the bike are a good 3miles from the wat itself.
I loved it. I don't think I would travel just to go to Cambodia though. So think about extending your trip to somewhere else?