I was there last Nov/Dec and it's an amazing experience. People are so friendly, and easy to get around. I stayed at Le Meridien and was really nice. Loved the pool.

As far as how many nights, like others are saying, I'd stay at least four nights, but it depends on how interested you are in the temples. How many and how deep do you want to see them? There are lots of sites, most of them in the Angkor Wat complex but there are some others + Land Mine Museum (small but interesting) over one hour drive from Siem Reap, which I thought were worth it. We had a private tour guide which took us to all the temples, really nice guy. Do you have one? How are you planning on getting there? Guides are worth it there, and not that expensive. I'd recommend hiring one with an air conditioned car and not tuk tuk, it gets really hot and coming back to cool air was very much needed.

More than happy to give you more info should you need it, PM. Enjoy Cambodia!