I've been a day-to-day Rakudo user since 2008. Here are the things I really like:
- Classes and roles, available out-of-the box.
- where clauses and subtypes. Pretty.
- Grammars. Easy to parse just about anything.
- Meta-operators. It's fun and easy to think composite thoughts with a single line of code. And it becomes second nature quickly. I miss it in Perl 5.
- Multisubs and multimethods. Just plain convenient.
- Gradual typing. The types stay out of the way when I don't need them, but are there when I want it. I can choose to give a variable a type or not.
- Neater syntax generally. Some things just read nicely in Perl 6. I never thought Perl 5 would feel like boilerplate, but in some cases it does after writing lots of Perl 6.
Things I still miss:
- Heredocs. Niecza has them. Rakudo doesn't.
- Shaped arrays and hashes a la Synopsis 9. Some multidimensional primitives related to this.
- Speed, generally. We got faster at startup recently (jnthn++), and it makes a great difference. Niecza is faster than Rakudo once it gets going. But we still have ways to go in terms of performance.
- Call me impatient, but I want the vision of mutable grammars, and a plug-and-play Perl 6 where you can add your own parsing rules or sublanguages, to come to fruition as soon as humanly possible.
- Things need to get a lot more polished. A lot of the bits are in place now, but we're disorganized in terms of documentation and in terms of helping a newcomer become productive. We're very grateful for all the feedback we get from newcomers; the early adopters sandpaper the barrier to entry and make it easier for their successors to just pick things up.