I am an something of an amateur WW2 historian but found the story disjointed and boring, the flying scenes are authentic and some of the best flying WW2 CGI I have ever seen.
I found the the POW episodes from Stalag Luft three based on my previous research interesting and authentic, I think the high rating on IMDB is because people are acknowledging the detail and work that obviously went into making it, as entertainment I would rate it around 6 or maybe 6.5
I have visited sites of many of the USAF and RAF bases in East Anglia, very little now remains of most of them, most having been tuned into farmers fields, many do however have a plaque marking the spot.