Yeah, they do send a chill down my spine during late night theiving with the lights off, in that regard they are effective, but I just HATE dealing with shit that either can't be killed/avoided/or wastes an assload of bullets.
I'm a huge fan of Thief I, sorry to say I never managed to get a copy of Thief II, so I can't judge it. But after experiencing RTCW, I said to myself, NO MORE!
NAZI's are much more satisfying to "silence" (that that as you will) than something that's already dead and doesn't know shit from brains anyway.