Language
The characters speaking in German, Dutch, etc. throughout the film, rather than the oft-used device of a smattering of words in the foreign language, then reverting to English was a plus in my book, though Peppard didn't really sound as convincing as the other two agents, Courtenay and Kemp.
I suppose its a thorny issue for filmmakers; try to be authentic as possible when making pictures or stick to one language and rely on viewers' suspension of disbelief.