I like this show. It grows on you. It has now whizzy special effects and if you want those, watch the Tom Cruise film. The tension here is that you don't see the aliens. Throughout you are left wondering who they really, why are they here and what do they want? It is a drama about people and what they might do facing the end of the world.
Good cast with plenty to work with and they bring out the human element to the story. Dramatic tension is maintained and there is a haunting soundtrack. Interesting British/French co-production which brings out the idea that this is something across the whole world and not just a corner of it. If you feel it is a bit slow at the start, stay with it. It's worth it.