The title of this series 'Celtic Britain, should really be called 'Ancient Britain Part 2, as it is a direct follow on from Neil Oliver's previous series. Picking up from the end of the Bronze Age we learn about Iron Age Britons and the impact of the Roman invasions on british society. If you liked the first series then you should like this, with Mr Oliver continuing to exude almost over the top enthusiasm for his subject matter. Other reviewers have said that the 'ancient/celtic britain programmes are a lazy form of learning and this is very true but these documentaries are introductions. If you want to delve deeper then you can always read a book on the subject.
Perhaps Neil Oliver will make one more series. "A History of Dark Age Britain" starting with Post-Roman Britain and ending with the Norman Invasion. That would be a great way to round off the series.