In the COM API, properties are usually simple built-in types, such as double, or types such as BSTR that map to built-in VBA types such as String. In the .NET API, most properties are one of the Property* classes that implement the IProperty interface. For these properties, you get or set the Value of the property. For example, this code in COM:
oLabelStyleLineComponent.Visibility = True
oLabelStyleLineComponent.General.Visible.Value = true;