We sepnt a few hours here after seeing the Great Wall in the morning and wished that we had had more time. We were there late November 2006.
You do not need a guide, the place is easy and fun to explore on your own. If you like parks and park architecture, follies, arches, gazebos, etc., this is the ultimate Chinese park. Supposedly the Empress Dowager Cixi spent the money earmarked for a navy on luxurious pleasure palaces like this. It sounds foolish, but her in her view, a Chinese navy might defeat one rival nation's navy but there would always be yet another navy to fight and ultimately be defeated by. Instead she thought lavish palaces would impress foreign dignitaries who would then treat China with respect. Such was the self-centered naivete of China's rulers during its repeated 19th century humiliations. (Well, China's back, isn't she? What's a couple bad centuries out of 30.)
The grounds are beautiful and very extensive, some forested, many with lawns, and perfectly restored buildings all over the place. This is what the Imperial Garden in the Forbidden City wished it could be. The Long Corridor is astounding--thousands of decorative paintings and the thing is about 1 km long. The hill overlooking the lake is covered with small temples. I climbed up part of it, but didn't have time to see everything.
You can boat on the lake in warmer months or take ferries that go to a small island. There is also a beautiful long walk along a chain of islands connected with different types of bridges. Signs by the trees say that they were planted during the Kangxi Emperor's reign--the 18th century.
We arrived too late to eat in the one restaurant in the park, I have no idea about its quality. There are several shops selling snacks and cup-o-noodles, which we ate instead, and the staff thoughtfully cleared a table in the shop for us to eat at...this was November so obviously not the high tourist season. As navigator stated in his/her review, bring some food in or be there before lunchtime. There may well be more food vendors in warmer months.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.