This was the one that made me a Perl 6 convert! Up through A3, I was "unsure". With A4, I thought, "This could be OK." A5 made me stand up and yell, "Hallelujah!" (After which I had to convince the other people in the office to let me up off the ground....) I haven't gotten all the way through it even now, but I'm very impressed so far.
I use regexes a lot, and frankly, I hate the existing syntax. Simply recognizing that regexes are programs with an awful grammar ("They're programs, not strings") is a big step forward. Regularizing the interpolation rules and bracketing constructs is a great simplification. And I love the changes in the semantics of what constitutes a "line", the use of ^ . \Z and so on. It seems like every time I need to use /s or /m, first I have to go read perldoc perlre again to remember which is which.
Kudos to Larry for the guts and insight to replace an old crufty structure with this beautiful edifice. I have a little bit of precious free time coming up, and this convinced me to spend it helping out in the effort, doing whatever is needed.