For a mid-term zombie film, it was inventive (Cornwall mining setting, etc.), but I did find it slow-moving, and certainly there have been many more impressive zombie features (as well as much more icky zombie features) done since then, including Gilling's work on one of the Blind Dead features.

The laser disc surprised me as I believe the first couple of reels were switched, so that the pre-credits sequence appeared right after the opening credits instead of before.
Then again, I once watched a 16mm print of DEMONS OF THE MIND where a couple of reels had been spliced in the wrong order.