Logic and syntax are (nearly) unchanged. Also I'm currently not aware that any features/functions are disabled else there are just some new ones. Therefore most of your stuff should further work smoothly.
But it may also depend on applied syntax. There were for example some bug-fixes to the quotes-handling within variables and set analysis which accepted before an invalid syntax (beside the valid one) as valid and nowadays it leads to wrong/missing results.
Beside from script and expression they changed the printer, the GUI rendering, the IE plugin support and probably some more which may lead to issues if your upgrade happens on a also quite old machine respectively OS - whereby I seriously doubt that remaining of them would be sensible.
Why not just trying the new release in parallel - at least partly - before upgrading your environment.
- Marcus
