The plot is simple – an unexplained world-wide epidemic that robs everyone of their sense of smell. Just as people are adjusting to this, taste follows.
The story is told mainly through the relationship of two lovers, played by Eva Green (Susan) and Ewan McGregor (Michael). Strangely, although Susan is an epidemiologist, the story doesn’t advance very far on the science side, as they are pretty much stumped. However, Michael’s career, as a chef, allows for an interesting examination of how people adjust to change. As such, it is more a social study than anything else.
However, I found it engrossing, although people who like their sf a little harder may be disappointed. Elsewhere, I have seen the film described as a little like John Wyndham, and I think that is pretty fair.