Might seem to be a bit stingey only giving this four stars but it's simply because I have to compare it with The World At War, the seminal television treatment of one of the worst episodes in human history. Apocalypse really is an excellent documentary series but it's only a few episodes and to deal with a World War stretching (for Britain) from 1939 until 1945 and which was conducted across several fronts world-wide, over several years by many nations is bound to mean that some campaigns which loom large in a nation's psyche, such as the Battle of Britain and D-Day are dealt with only briefly. Nevertheless, as a kind-of 'potted' history of the main events of the war which resulted in the most relevant changes in the balance of power, this is excellent and informative viewing and I recommend it to you.
If this whets your appetite then go one step further and get hold of the World At War. It has the privilege of being delivered over what amounts to many hours of viewing and to an extent, this is what Apocalypse has to recommend it, it does it well with brevity.