Typical Venoms-era Chang Cheh really - paper thin plot that somehow still manages to be convoluted, even-thinner-than-paper characters, awful acting, and entirely shot on indoor sets that wouldn't look out of place in a school play. Oh, and of course lots of kick-ass fight scenes!
I really hate it when people say "who watches these films for the story anyway?", because I actually do... but sometimes really good action can compensate for failings in other areas. The action in FLAG OF IRON isn't quite that good, but the film has some other redeeming aspects too (like Lung Tien-Hsiang's sideburns) and is generally an entertaining watch (though sometimes you're laughing at, not with).
Not quite a good film, but can't bring myself to call it "bad" either. Worth a watch if you like Chang Cheh's Venoms-era films, basically.