1. DTD allows only to constraint your elements structure and does not validate element contents. Whereas XML Schema will allow to contraint element structure as well as element content.
2. DTD is not XML where as Schema is XML. so it is convient for XML designer to write schema than DTD as writing DTD will involve understanding different syntax altogether.
3. The largest addition XML Schemas provide to the functionality of the descriptions is a vastly improved data typing system. XML Schemas provide data-oriented data types in addition to the more document-oriented data types XML 1.0 DTDs support, making XML more suitable for data interchange applications. Built-in datatypes include strings, booleans, and time values, and the XML Schemas draft provides a mechanism for generating additional data types. Using that system, the draft provides support for all of the XML 1.0 data types (NMTOKENS, IDREFS, etc.) as well as data-specific types like decimal, integer, date, and time. Using XML Schemas, developers can build their own libraries of easily interchanged data types and use them inside schemas or across multiple schemas.