I had never seen Survivors before, but I had heard of the basic premise of 99% of the population being wiped out by a virus. This sort of post-apocalyptic story has a robust tradition in British minds - witness 28 Days Later and The Last Train. But I think Survivors is the best example of this "end of the world" scenario.
Nowadays, it seems all the dramas on TV are either concerned with the police, hospitals or other public sector workers like the army or fire brigade. Survivors cuts through all this and simply deals with human nature and its many faults and shortcomings.
There are 13 episodes in the 1st series. The 1st episode "The Fourth Horseman" depicts the spread of the virus and is fantastic in its pace and scope. The other episodes are all gripping, but special mention must go to the 9th episode "Law and Order", which made me feel physically sick at the end. This was not because of any violence but due to the concealment of a miscarriage of justice that shook you to the core.
I also have to mention that it makes a refreshing change to watch drama that does without overbearing incidental music. There is no background music whatsoever in Survivors and it adds to its "naturalness", if that is the correct adjective.
Overall, Survivors is great, thought-provoking television. Just be aware that some of the thoughts provoked can be quite depressing and rob you of a good night's sleep.