There are many good reasons to use ANSI join syntax instead of the old Oracle join syntax. With one exception: If you want to use your Materialized Views for Query Rewrite, avoid to write them with ANSI joins.
Foreign key constraints are often omitted in Data Warehouses. This blog post explains why this is not a good approach and what is a practical compromise for foreign key constraints in an Oracle Data Warehouse.
Partition Change Tracking (PCT) is a powerful feature in Oracle for fast refresh of materialized views when one of the base tables is partitioned. But under certain conditions, PCT does not work as expected and returns an unpleasant surprise.