There’s a neat little change to the Automatic Diagnostics Repository (ADR) in Oracle 12c. You can now track DDL operations and some of the messages that would have formerly gone to the alert log and trace files are now written to the debug log. This should thin out some of the crap from the alert log hopefully. Not surprisingly, ADRCI has had a minor tweak so you can report this stuff.
You can see what I wrote about it here:
Of course, the day-to-day usage remains the same, as discussed here: