Very fun and lots to do !
As I was coming from Shanghai, Beijing wasn;t as imposing, but it was very fun. Reserve at least 4-5 days as some 2 or 3 main things you should see there take one whole day each. Avoid the little tuk-tuk looking vehicles as they aren't really trustworthy and my friend got scammed for $YN300 in one. DO take the cable car for the Great Wall if you go to the section with it as it saves almost one hour each way instead of walking up the side of the mountain.
Insider Tip:To avoid crowds around Tiananmen Square just get off a metro stop or two down the line. If you are a student, bring your passport copy and student Id as we enjoy discounts at least 50% off to most attractions, sometimes even more than that !