What a poor position for voters: The current govt who announces campaign policy it has no intention or capability of following through on and can't be trusted, or the opposition who is changing leaders every five weeks, can't articulate any policy that isn't a road and can't be trusted.
To be fair to the current government (and all governments in MMP). In a campaign you are showcasing the policy you would enact if you were the government, ie if Labour were in a one party government and had a majority. The reality is that on election day, the government is formed by multiple parties - so you will by necessity always end up with something different to what was pushed on the campaign trail. It's just the reality of MMP.
The same is true of any MMP government. We didn't necessarily get what National had campaigned on in their previous terms, because they had United Future and the Maori Party influencing the policy that came out. In fairness, Labour have it worse on this front because they have less seats - so they actually need their coalition partners to get things through - which means the government policy will be markedly different from campaign policy.
That said, there are some obvious losses from the current government that aren't necessarily excusable by the above statement. To say they can't be trusted is unfair and untrue though.
Labour was always going to go into coalition involving the Greens and NZ First if they wanted to govern. I've made this point before. Campaign promises can not suddenly disappear because the slate magically gets wiped clean when you enter a coalition agreement; people who voted for you did so on the expectation that you would make certain things happen. We don't let companies do it it - it's called 'bait and switch' and regulators take a very dim view of it. Labour was always going to require the support of the parties it ended up in power with - to turn around and blame them for things like Light Rail (which was derailed by two years of incompetence before Winston nixed it) is trying to play a get-out-of-jail-free card for being accountable to the people who elected you.
Otherwise, you're making a case that parties should be able to promise whatever they like with no imperative to deliver it. That totally undermines the idea of an informed voter casting a vote for someone to represent their interests, which is the basis for how democratic governments are elected and derive their mandate. If it were "vote for us and then we'll spend three years doing whatever we want and we don't feel obliged to do anything we campaign on" then I suspect you find that a substantially harder sell to the voting public.
The other aggravating factor is that we are not talking about a couple of things here and there, we are talking about nearly every flagship policy - including ones they had used a platform to (rightly) attack the incumbent government for 'inaction'.
E: I should point out that I feel National and Labour have a higher moral imperative to campaign on 'real' tangible things than the fantastical nonsense that ACT or the Greens put up - the policy concessions should flow from the major parties to the minor parties, not from the major parties into the ether because their basis for getting votes was actually totally unworkable.