Actually I'm impressed from the speed (even so it is a Java based application), the easy handling and the integration into APEX.
For example remote debugging possibilities inside an APEX application: http://www.oracle.com/webfolder/technetwork/de/community/apex/tipps/remote-debug/index.html
Currently there are two things I really don't like.
Autocomplete Feature when I open a table and checking the data.
If I click on the autocomplete it sometimes adds it at the end of my text. Instead of dropping my text and replacing it with the autocompleted text.
View with Trigger
When I use a view with an InsteadOf-Trigger and later I need to update the view. With the SQL Developer View Editor actually it does delete my Trigger. Even the Fast DDL feature does not include the trigger. Hope this is fixed in the next version?
My workaround is to add the Instead of Trigger as Comment behind my the sql of the view.