I visited the Imperial Palace in Beijing twice. Once in 2006 and once in 2007. A true exploration of the site runs about half a day. It is worthwile to explore the side sections of the palace. Each side passage or courtyard reveals something new and is quite interesting to search in depth. Moreover, large restored sections of the palace are being opened every couple years. Suprisingly, vast sections of the palace are still closed and are scheduled to be revealed to the public in the not too distant future. Try not to visit the palace in the summer or weekend if possible as it gets clogged with people (literally).

The tile panels are certainly a highlight, and side alleys have a more personal atmosphere that you don't find walking near or around the central axis. I prefer weekday mornings, if you are lucky with the smog, the pictures can be incredible.