The movie, which follows a different group in Wellington, New Zealand, is excellent and I highly recommend it if you haven't seen it before. If you love the movie, you will love the show! What makes the show better than the movie comes down to the episodic nature of television. The episodic format means plot-lines can begin and end more quickly than the movie, characters can be developed more and they can be thrown into a wider variety of crazy situations. The movie had great world-building but could only do so much with an 85 minute runtime, and the show furthers that simply from having more time.
The show would not work if Taika Waititi and Jemaine Clement, who wrote/directed/acted in the movie, were not onboard. They ensured that the tone, production design, shooting style, and humor were all on par with the film. Thank goodness season 2 is on the way!