The major diffferences are-

In 9i merge , insert all, case is introduced .

In 9i newdatatype called timestamp

In 9i you can moniter index using alter index <index name> monitering usage

or

u can check user_objects table from system user.

In 9i new performance monitering tools called STATPACK .

In 9i You can dynamically change init ora parameter using alter system <parameter> scope=/path/ of your spfile/pfile

In 9i new concept for undo transaction called UNDO tablespace

In 9i by default   TEMP tablespace  is considering while creating new oracle users

In 9i new partition called LIST

In 9i tablespace next extent can be managed automatically

regrds

rajat dey