I saw it in theater.  i also did a fair amount of reading on the subject first.  No, it doesn't have the feel of Private Ryan or Band of Brothers.  And it shouldn't, Dunkirk was not the crusade to free millions of oppressed people from the Nazis,  Dunkirk was thousands of men waiting for dozens or hundreds of hours in vast confusion.   It's a rather uncomfortable film to watch, but it conveys that experience pretty well. 

The RAF actually gave pretty effective cover and gave a good account of themselves over Dunkirk.  They were still struggling with things like not giving up the pre-war ideas about tight V three ship formations, but they were learning things that paid off in the Battle of Britain shortly following.   And it was the first large scale use of the Spitfire, only Hurricane squadrons were deployed to France in 1938-40.