So who's right?
How it works
MMP gives voters two votes - one for their preferred political party, and the other for the MP they want to represent their electorate.
Parties have to get a minimum of five per cent of the vote or win at least one electorate seat to get its share of seats in Parliament.
Parties rarely win enough votes to govern alone, and coalitions are a common feature of New Zealand governments.
The result is a Parliament in which a party's share of seats largely reflects its proportion of the national vote.
Until MMP was voted in in 1993, Kiwis had one vote under FPP - a system where candidates with the most votes won, regardless of whether they had 50 per cent.
Major parties tended to win a larger proportion of Parliamentary seats than their share of votes, while smaller parties were largely sidelined.
Electoral shake-up
Catalysts for electoral reform began to stir in the 1950s when public confidence in politicians and the two-party system began to erode.
Over the following decades, economic uncertainty and social upheaval helped give traction to the idea that Kiwis weren't being represented accurately.
Despite winning decent chunks of the vote, many smaller parties were being excluded from Parliament altogether, causing significant voter disillusionment.
Canterbury University political science lecturer Dr Bronwyn Hayward says many people felt FPP unfairly inflated the vote of some parties.
In 1993, Kiwis voted in a referendum to change the voting system to MMP - marking the country's biggest electoral change since women got the vote a century earlier.
The overhaul intended to give parties representation that was proportionate to their overall vote, and to give a voice to smaller parties and minorities.
But it hasn't all been plain sailing, and the looming election is bringing some of the biggest gripes about MMP to the forefront.
Perceived failures
One major complaint is the merits of the "coat-tailing" provision, which allows smaller parties that haven't met the 5 per cent threshold to bring MPs into Parliament on the "coat-tails" of an MP who has won an electorate seat.
The clause also permits larger parties to forge deals to help smaller parties over the line, such as National's deal with ACT in Auckland's Epsom seat in 2011.
Former ACT leader and Epsom MP John Banks' infamous 'cup of tea' with Prime Minister John Key ahead of the last election has become synonymous with the practice, which many now want to see canned.
Following a 2011 referendum on MMP, which saw it retained, the Electoral Commission called for the coat-tailing clause to be thrown out.
Should they win the election, Labour is promising to abolish the coat-tailing clause within 100 days of taking office.
Another of MMP's controversial features is the provision known as "waka-jumping" - when a list MP is ejected from their own party but can remain in Parliament, collecting their salary despite no-one having voted for them.
Diverse community
Political science lecturer at Canterbury University Lindsey MacDonald says MMP made Parliament look much more like New Zealand, but this has had a double effect.
"It makes clear that we are a diverse community with multiple views on any subject and that in order to knit together a solution, everybody has to be included.
"But it's also raised and put in front of us that we're much more diverse than we're realistically comfortable with.
"MMP really shoves in our faces that politics is how we sort things. You have to have politics and you have to work with everybody."
The rise of transparency and representation has brought with it an unfortunate drop in voter participation.
Statistics New Zealand figures show voter turnout dropped from 88.3 per cent in the first MMP election in 1996 to 74.2 per cent in the 2011 election.
Put to the people
The public had their say in a national referendum on MMP in 2011.
While New Zealanders voted to keep the system, the referendum review included a number of recommendations on how the system could be improved.
These included an end to the coat-tailing clause and lowering the 5 per cent party vote threshold to 4 per cent. However, these have been largely ignored by the Government.
Justice Minister Judith Collins told Parliament last year that consensus was required for electoral reform, "and there is no consensus for any change".
But the decision to reject the recommendations was met with backlash from critics.
NZ First leader Winston Peters said last year that despite the expensive Electoral Commission review and its expert recommendations, "now [Ms Collins] has just canned the lot."
The Greens accused the Government of shirking its responsibility to voters and putting politics before the public, calling it "undemocratic".
Accountability
Ahead of the referendum, a group called 'Vote for Change' lobbied against MMP.
While the group has since dissolved, former spokesman and constitutional lawyer Jordan Williams still says the current system's fundamental flaw is a lack of accountability.
"Every system has its flaws but at least politicians think, 'I better do what the voters want otherwise I'll lose my seat'. The trouble with MMP is too often it's, 'I have to do what my party wants otherwise I'll get a low list position and lose my seat'."
Even though Kiwis voted to keep the system, we are becoming increasingly more "annoyed" with the political process, he says.
A good example of this is the recent union of the Internet and Mana parties.
"You've effectively got a rich foreigner [Kim Dotcom] who has created his own political play thing."
