As I could understand it *most* of the Perl5 syntax can be handled by Perl6 but not all of it, for instance a hash key is now written %h{key}. In general, contextual polysemy has been tracked and destroyed, this is what Conway calls Huffmanization.

Besides there are many new features that make the old Perl style verbose and messy in comparison. Youl'll find native
- iterators,
- Moose-like object constructors,
- generalized operators for method calls and parameter passing,
- type checking in subroutines,
- direct interpolation,
- subroutines trying (as in C++),
- overloaded and user-defined operators,
- and Unicode builtin.

This is why modules have to be translated in some way. One can find many modules - like CGI, DBI etc. - already available under the Rakudo project, unfortunately as far as I know Tk isn't imported yet, nor any other GUI.