This is really a must. The temples of the Angkor Archeological Park are truly awe-inspiring.
The complex is massive (250 square miles!!). Exploring the temples requires a ton of climbing and stamina, and the structures are far apart with little shade in between. So unless you are an architecture buff, one day is plenty!
Since there is so much info online about all the temples, I will spare you the details. I would like to note that the day pass begins at 5pm the day before, so you can watch the sunset and get yourself amped up for the following day. A great way to avoid the throngs of people is to skip the sunrise at Angkor Wat and instead, begin the morning with some of the other temples. I can't recommend this enough! We were able to stay one step ahead of the crowds, a much more enjoyable way to appreciate the architecture of the ruins and the sheer scale. Catching the sunset the night before also allowed us to leave earlier, because by late afternoon, we were so exhausted and sweaty, the last thing we wanted to do was wait until the end of the day.
After lunch, we made one last visit to the main temple, before taking off. The late afternoon at Angkor Wat is another time to avoid the crowds as they're still exploring other temples and haven't yet returned for the sunset. Walking along the cool stone corridors with beautiful golden light streaming in, surrounded by silence, was so peaceful and meditative.