Depends on your definition of 'easier' and 'better' really since that's a nice solution (although it should probably check the return of ref). Perhaps ...

sub flatten { map { ref $_ eq 'ARRAY' ? flatten(@$_) : $_ } @_ }

print join ', ' => flatten 1, 2, [3,4], [5, [6,7, [8,9] ],10];

__output__

1, 2, 3, 4, 5, 6, 7, 8, 9, 10
[download]

But we're just golfing now.