We had 3 days in Siem Reap, which was just not enough time. The temples are amazing, definately a must see. But, for us anyway, two days of temples were enough. We enjoyed spending time in the town, driving around the countryside, and interacting with the locals much more. They are a wonderful group of people, and are sincerely happy and proud of their beautiful country.
Quick Tips:
Good to have a guide for the first day or two of temple exploration, but after that it would be good to go it on your own...to take your time and get your own experience out of it. It seemed like a long ride from town to the temples to take a tuk-tuk ride there, better off in a car. Try not to get anoyed or be rude with the kids selling things outside the temples. They don't like to take no for an answer, and can be persistant...but they respond well to kindness and a smile, and you can have fun with them if you try.
Best Way To Get Around:
We hired a personal guide for the temples, your hotel can help you find one. Probably best to arrange this in advance. For getting around in town, either walking or a quick 2 dollar tuk-tuk ride can't be beat.