It implements the SQL standard very well It includes support for "advanced" SQL stuff like window functions or common table expressions It is very innovative in

It implements the SQL standard very well It includes support for "advanced" SQL stuff like window functions or common table expressions It is very innovative in terms of how plpgsql interacts with SQL It supports lots of advanced data types, such as (multi-dimensional) arrays, user-defined types, etc. These are pretty good reasons :)