Saw this last Tuesday night, very well done. The voice overs were from actors from the relevant areas of the UK as the Veterans themselves were unavailable to voice themselves. However apart from the voice syncing of the footage the whole film was 'real' in that it was shot between '14-'18 and the commentary was recordings of the veterans made in the '60s.
The film never looked at the bigger picture, no grand scheme was discussed, it was just about the man in the mud and what he was experiencing. And according to the film mostly it was fun, a great adventure, " like a great big scout camp with a bit more excitement" was one quote IIRC. I was particularly interested in how the troops felt about the enemy, and it was not always as I expected, and the thoughts of some Germans towards regiments from another part of Germany was revealing.
It was a great watch, very moving in places and the renovation of the footage made it very real and up to date. There was an interesting Q&A with Peter Jackson after the showing. The original films were cleaned up of 'noise', slowed down and the missing frames were digitally inserted before colourisation, Jackson has over 100 hours of remastered footage (in B&W) and as he's a great history buff he said if anyone sends him the raw film he'll do it for free.