Utterly boring and silly. Spitfires that fly forever, even after the engine is out of fuel. Other than the very few German airplanes and perhaps a submarine there were no Germans to be had and essentially no combat. The real story has about 850 small boats rescuing the soldiers. The movie has, at most, about a dozen and really only focuses on one. And that one may have gotten lost at sea, as the crossing is less than 40 miles and seemed to take forever.
The scene with the soldiers in a sinking boat was drivel. A ship that size being lightened by tossing one person overboard is ridiculous. Further, every round they took was below the water line? Just silly. And several feet of water being taken in only a few minutes from a few small bullet holes? Even sillier.
The characters were, at best, wooden. Meaningless dialog, when there was any. No sense of tension (ok, we all know how it was going to turn out - but as the characters were so 2 dimensional - who cared about any particular one?). Nothing in the way of humour or wit.
I'm not really sure how one can take such an interesting (real) story and produce such a boring representation of it.