It is particularly "realist" in it's style which you have to get used to from a modern perspective - but it's very, very much worth it if you can get into it. It's generally considered a very important television series here from a "golden age" and it's very historically accurate in terms of plots and characterization as it's made at a time where many of the parties involved in the real thing could be set consultants. David McCallum actually went with the real escape officer back to visit as a sort of accuracy reccy.

Personally I think in terms of characterization it's the best work McCallum's ever done - he makes interesting and unexpected acting choices and his character has a fantastically nuanced development arc across the two series.

However, the realism and the nuance does require commitment.