Object-oriented GIS design is easy
All the complexity of feature classification and validation is in the shared repository.
Relatively 'thin' clients can be quickly built for many specialised purposes.
Notes:
The marketing message is that constructing a GIS application with OO GIS involves a great deal of work designing the geo schema and methods, and then a relatively 'thin GUI layer' is written for the client.
This is true from the point of view of the GIS information, but is misleading from the point of view of the client developer. Modern human-computer interfaces are sophisticated applications, built from a combination of hand-coded, bought-in and operating-system-supplied components. Ease of use and transparency for the end-user is achieved by complex software which hides and transforms the underlying lower-level technology.
Encapsulation, inheritance, polymorphism etc. are like just learning about nouns, verbs, adjectives. Constructing an OO system is like writing a best-selling novel: the important issues are plot, characterisation, narrative flow, building suspense, action and a satisfactory 'shape' to the whole story. What you have been told up to now about OO is just the nouns, verbs and adjectives...