Back in September, I warned against a three-strikes law that eliminated marginal deterrence. It looks like ACT and National have come up with a compromise that sounds pretty sensible. There's a list of serious "strikeable" offenses. On the first strike, the offender is warned that it's his first strike, with sentencing as normal. On the second strike, "truth in sentencing": no parole period applies, so the offender serves the full sentence. On the third strike, the judge must assign the maximum sentence, again with no parole. Since the only penalty for murder is life in prison, murder as a second strike gets the same treatment as murder on a third strike.
This makes much more sense than ACT's initially proposed "twenty five years for a third strike" rule, which of course eliminated marginal deterrence across third strike offences. There may still be a bit of a severity shift within categories: offences within the same category can be more or less serious, but the losses from this kind of shift are pretty small relative to the losses from a blanket "25 years" policy. They also ought to be small relative to the deterrent effect achieved.
Recall that California's three-strikes law deters even first offences on the strike list. The NZ law seems to avoid the biggest problems of the California legislation: there won't be any serious severity shift the way it's written, and the increase in prison costs will be rather smaller than that experienced in California where any third strike draws a fixed and long sentence rather than one proportionate to the offence committed.
Note that strikes only count going forward; this also is pretty reasonable.
Good job ACT and National. I'll be interested in seeing the full list of strikeable offences and the rest of the details, but this gets a big provisional thumbs up.