I'd live there too if it wasn't literally on the other side of the planet for me and I don't want to cause hundreds of tons of CO2 every time I want to see my family :'(
Food - groceries are pricey! It was surprisingly expensive given the lower wages here. CA seems to be catching up though!
Mosquitoes - comparable to LA, less than Sonoma County. Smaller too. But here on the South Island we also have sandflies. They vary by region. West Coast has them bad in some remote spots.
The food is generally excellent in urban areas - cafe culture rules for those who can afford it.
Main issue is cost of living - housing and food costs are kind of silly relative to average income.
Mosquitos are really not an issue - people up north might have a different experience, but from Auckland on down, no one needs screens.