Whilst the Summer Palace does not compare to the Forbidden City or the Great Wall, it is still an impressive site. As with the Forbidden City it is over-run with tour groups, but a little bit of effort climbing up to some of the more 'remote' parts of the site will reap rewards.
Whilst parts of the Palace were disgracefully vandalised by Anglo-French forces, it is interesting to note that more recent damage, from the Cultural Revolution (mainly the damage to the Buddhist section) is unrestored (and the blame unapportioned).