I have seen "Flags" and it was very good.. I'm excited to see "Letters" as well.. I love WW2 movies and have seen just about all of them, old-new-good-and bad. By far my favorite is "Downfall" its a subtitled German film (ala Das Boot), and if you guys haven't seen it.. I highly recommend it!
A link to the trailer if anyone is interested
http://www.rottentomatoes.com/m/downfall/trailers.php