Compare the lack of quality of the production for the unreleased RCA album, including tracks such as "Transmission", "Novelty" and "Shadowplay" with the later re-recorded versions under the production and direction of Martin Hannett. Bear in mind that these recordings were barely a year apart. I admit that the songs might also sound better as the band got better musically, but I think that MH deserves maximum credit for his contribution.
Then also compare the RCA album with A Factory Sample, although obviously the songs themselves were different, "Digital" and "Glass" which were recorded and produced by Hannett six months after the RCA sessions have a far superior sound quality.
In my opinion Martin Hannett was crucial to the success of Joy Division, as he introduced the band to synths, which they had previously rejected a year earlier when they thought they were (just) a punk band. Had he not done this JD could have fallen by the wayside by the end of 1979, and its doubtful whether New Order would ever have existed.
As regards his work with New Order, both sides of their first two singles, and the extended "Everything's Gone Green" are absolutely fantastic songs with an equally excellent production.
Apparantly stories abound from the group that Martin made Bernard sing "Procession" or "Chosen Time" or whichever version of the story you've heard, MANY times before he was happy with it. This was in the days when Mr Sumner wasn't so much of a diva concerning his singing voice.
The major disappointment for me concerning "Movement" is that Peter Hook's voice is so poor on "Dreams Never End", now this is because either;
Peter can't sing; or
Peter deliberately sang that badly to avoid comparison with Ian; or
Bernard didn't want to sing the first track on the album.
Its not down to Hannett as had the band or Factory been unhappy with the production on the album or any one song on it, they could have rerecorded it (like "Ceremony"). I think Hannett gets wrongly accused regarding "Movement". The album is not an easy going one, it never was going to be in the circumstances but it is an important document as it marks most of the songs written in the immediate aftermath of Ian's death.
For me though Hannets work with New Order in 1981 was when the band were at their consistent peak, although there were other returns to form in the intervening 20 years.