One of my favourite places thus far in China.  It is famed for its canals and gardens.  Chinese gardens are supposed to show the balance between different elements and provide peace.  With this is in mind my advice is go early.  Get there as they open because once the tour groups turn up there will be a fat chance of either peace or serenity.  
The old town with the canals running beside mostly pedestrian streets is also pretty good.   A nice place just to wander have a coffee and wander some more.