I knew one man who was a WWII POW in Germany. He said that the Germans supplied some fairly advance math textbooks to them, as language is not so problematic with Math. Many of the POW's were pilots or navigators, so they took the books and taught classes on Math to those who were interested. He came out with a very high level of math knowledge during his time spent there.
He also commented that their food was no worse then the 'crap that the krauts ate', to quote him verbatim. All in all I never heard him complain of poor treatment, but then he did not discuss this aspect of his life very much.
My late brother in law, an infantry captain, was captured during the Battle of the Bulge. He later escaped, and didn't want to say much about it. He did say, though, that even though his dog tags identified him as a Jew, the Wehrmacht did not treat him differently than other allied POWs.