It's funny, but what seems to impress me most about some spy movies is when the hero has to do without the high-tech gadgets and gear. The only example that comes to mind is in Mission Impossible when Ethan Hunt breaks a light bulb and scatters the glass so he can hear someone approaching down the hall. I guess the reason it appeals to me is that these are things I could conceivably do. That other stuff, whether it's computer-controlled guns, acrobatics or uncanny masks is entertaining but unbelievable too.
Mokalus of Borg
PS - It's as if you find out how good a spy they really are when you take away their gadgets.
PPS - Maybe that's why Casino Royale impressed me, too.