We stumbled onto this program as my 3-year old son was poking around on Netflix Kids. He watched the first program and was instantly enthralled. It seemed pretty boring to me at first, but as I watched a bit longer I found it was surprisingly informative and engaging. My son has always been mechanically inquisitive, and this show absolutely resonated with him. The voice-overs are a perfect way to relate everything about the machines and the jobs they do. My son is now 4 and a half, and although Netflix only has 39 total episodes available to watch, he has seen each one at least a dozen times.
While it's fun to watch with them, and the kids certainly like seeing the big machines in action, the real thrill for me is catching my son later explaining exactly how the machines work. I'm sure most 4 year-olds will recognize a crane, but how many will tell you what the counterweight is, and why it needs one? I know kids understand that steel is a metal made in a factory, but how many will give you a five minute speech on what "coke" is and how an electromagnet works? Of course much of this comes down to my son's personality and his interest in mechanical functions, but I credit this show heavily for feeding his voracious appetite. And bravo for doing it all without animation, cheesy characters, or products to buy (though he does have a substantial collection of construction toys now).