Well it's really badly played for one...bang bang bang.
Ouch, that's the composer performing it. Actually, I'm amused at your criticism of him, because I saw him give a solo piano concert and he took a full, slow, low bow after every short piece as though he were the greatest pianist on earth, which he clearly is not.
I really like this piece (although my favourite from the soundtrack to
The Piano is actually "Big My Secret"). It's important to bear in mind, though, that Nyman wrote the music to the film bearing in mind the technical and musical contraints to which the central character, Ada, might have been subject. Nyman himself was certainly able to compose more complex and demanding music than that: consider his
Zoo Caprices for Solo Violin, for example. I believe that Holly Hunter performed the piano pieces shown in the film, so in this case the restricted difficulty level was to the benefit of the film makers.
I don't see, however, why ease of performance should be regarded as a weakness in any piece of music. There is a lot of beautiful music that is easy to perform, and there is a lot of complex music that is supremely tasteless.