Hi,
Your JSP's should still work, as should your classic UI components. If you want to move to Touch UI, you have to rewrite your dialogs. (can't remember if the migration tool was SP2 or 6.1)
Please review the documentation for backwards compatibility [1][2]
You can find out about API differences here [3]
For your maven dependencies, there is a new uber jar which does away with the many dependencies you had to use in 5.x [4]
As we don't know what is in your codebase there is no way to determine if it will run as is. Hence the need to review the documentation. There are some things that you will probably have to change such as admin sessions [5].
Also check out this Deep Dive into AEM6 which covers backwards compatibility[6].
I'd recommend taking your codebase and deploying it to a AEM6 instance and see what happens and run a full suite of regression tests. Alternatively, check your dependencies and update them to AEM6 dependencies and see what code compilation issues you get.
Regards,
Opkar
[1] https://jackrabbit.apache.org/oak/docs/differences.html
[2] http://docs.adobe.com/docs/en/aem/6-0/deploy/upgrade/introduction-to-oak.html#What%20is%20different%...?
[3] https://docs.adobe.com/docs/en/aem/6-0/develop/ref/diff-previous/changes.html
[4] http://blogs.adobe.com/experiencedelivers/experience-management/aem6-maven-dependencies-simplicity/
[5] https://cqdump.wordpress.com/2014/06/23/aem-6-0-admin-sessions/
[6] http://dev.day.com/content/ddc/en/gems/technical-deep-dive-of-the-aem-6-platform.html
