If you had to give up one of your senses, I think the vast majority of people would probably end up going for smell. Not to say it is not necessary, but just that most of us take it for granted. The strength of this film is that it relates how hard it is to actually lose it, and what is lost by it happening. Mostly the film is talking heads, but they are sharp, come across well on camera, engage with their subject, and are genuine in whatever they are saying and how they are saying it. This aspect of the film is the most interesting, and I was held by this.
Structurally the film mixes in scenes and images to avoid just showing people in a room talking. These image though are scenes that immediately capture a smell – grass being cut, for instance. They are beautifully shot, are so rich in color and movement, that the viewer can almost smell them – or at least are reminded of how great it would smell to be there. This is a simple device, but it is very effective because it pushes us to appreciate smell, while at the same time hearing the loss of those that don't have it – the mix of these two things increases the impact of the documentary.
It isn't earth-shattering perhaps, but it is engaging, looks great, and makes it point well.