Don't blame the electoral system. Our problem in NZ is clearly the ideological one-eyed-ness of some of the contenders - particularly of the Green party, but as well - in a smaller capacity - of ACT.
MMP works really well if you have a number of players who all try to focus on implementing as much as possible of their declared policies in government, able and prepared to work together with a number of the other players to achieve their goals.
It works less well if you have a bunch of players who are already during the election race connected by the hip to some of the other players - this makes the running much more difficult and makes the mix and match process afterwards nearly impossible.