Spoilers abound in this discussion of how men and women are treated in this movie. Don't read this if spoilers and frank discussion bother you.
The movie's strength, beyond its fascinating camera work, is its view of the unusual relationships between the three people. Like The Age of Innocence, the central conflict in the film revolves around the way people fight social conventions. In The Age of Innocence, most of the fight was internal. In The Piano, the fight comes into the open and the "baser instincts" win.
The Holly Hunter character has already broken a major social taboo by bearing and keeping a child out of wedlock. In returning to her family home, she becomes mute---one of her only weapons against the family she clearly resents. She permits herself to be used like property by going into an arranged marriage. (I missed the very beginning of the movie, so I may be misinterpreting some of the set-up.)
The Sam Neill character represents "civilization" on the frontier. While arranging for marriage and treating his new wife and her possessions as property, he is very Victorian and does not force himself upon her, "as is his right." He waits for her to become "more affectionate" towards him, and generally treats her civilly except for his using her piano as a bartering chip. When he finally cracks, it is expressed in physical violence (but not sexual violence).
The Harvey Keitel character is the "bridge" between European civilization and the Maori, as well is being a sort of "sexual bridge." At times he behaves brutishly towards Eda, but he never really does anything completely outrageous. He is drawn towards Eda and towards her music. He bargains with Eda in ways that are appalling. But they fall in love despite their overly-business-like bargaining.
When Campion shot the erotic scenes in the movies, they were clearly from Eda's viewpoint. Neill, in particular, was something of a toy. Sex scenes in American movies are almost always focused on the woman, especially on her breasts, and it gets tiresome. Campion avoided these sorts of cliches.
While I don't agree this movie is "overblown," it is "weighty." The happy ending rather surprised me, because it played in counter-point to the near-tragedies earlier in the film (kind of the reverse of Thelma & Louise!).