I am going to make my comments about the series as a whole, not just series 7, as the arc of this series has been, to my mind, excellent. I shall miss this show very much.
Yes, the plot in series 7 was disjointed and it may not have been the best in the series, but the acting and the lead characters are just so well scripted and acted that i can over look much of this. I especially enjoyed Perez and 'Tosh', whom I really hope to see in future productions.
This is coupled with the setting in a place that perhaps few people have actually visited yet is so beautiful and haunting - coupled with such an excellent score.
Many seem to have thought this episode was less than great, but I have to disagree as it certainly held my attention and I found it difficult to 'solve' the murders ahead of time. So few clues! Yet the topic was one of current concern, and reflected the views of many, particularly young, people who are truly concerned with the future and the environment, even if they tend towards impractical solutions at times. While so may of us are just so complacent about the damage we are all doing to the planet and the high costs which will result in the future.
A truly great series!