I don't know about gems, but there are some that I thought worth my time.
"Theirs is the Glory" is a docudrama about Arnhem; interesting in that it was shot immediately after the war and heavily features the actual participants playing themselves.
"Gallipoli" – Not the Mel Gibson one, but an Australian miniseries starring Kodi Smit-McPhee. Follows not only a group of Diggers, but also the senior command and the journalists covering the campaign. Also, the New Zealanders get some recognition!
"April 9" – A Danish cyclist platoon faces the Wehrmacht. Based on actual events, and a very realistic, no frills look at small unit combat.
"Journey's End" – This one is a gem. One of the best WWI films I've ever seen.
"1939:Westerplatte" – The Polish garrison of Westerplatte resists the German invasion. No mythologizing or whitewashing here; there are some heroics, but it also delves into the disfunction in the garrison command.
"Battalion" – About the Russian women's "Battalion of Death" in WWI. Much is fictionalized, but interesting nonetheless, especially the factual parts.