Some New Zealanders don't like Maori imagery. Since it's impossible to represent all the ethnic groups of NZ in a flag, this flag doesn't have any red or blue (traditionally associated with Europe) nor any Koru or other Maori-esque imagery. It does however use the black and white colours which many New Zealanders have adopted for themselves. The green symbolises fresh-ness in environment and thinking. The silver fern used in this flag is more vertical than that used in sporting team logos and it is old fashioned so that it looks more like a fern than a feather. The Union Jack is also represented in this flag in white in recognition of the ties with Britain that NZ continues to have.
In minute thumbnail size it seems to look like a smear of some sort (a squashed insect?). But the colours are unique enough to be recognizable even when the flag is furled.