Reddit mentions of Mazinger Z TV Series Part 1

Honestly, you're not missing too much. While it is fascinating to see the origins of super robot anime, it's poorly scripted, it drags HARD through most of it, and it's mostly just monster-of-the-week with very few episodes ever advancing the overall plot. There's probably a way to condense the series down to 15-20 episodes without skipping anything of note.

That being said, Mazinger Z is licensed in the US by Discotek Media, and not (legally) available for streaming. You are unlikely to find it used for cheaper than $80 for both box sets together.

DVD Box 1

DVD Box 2

I don't know if it's legally available streaming anywhere, or illegally available in some form, but I know Discotek are bringing out a North American DVD release at the moment (only the first half is out, I think). Obviously still a pain for those of us, like me, who aren't in America but it's something.

You might be interested to know -- if you don't know already, in which case sorry to bring it up -- that there've been several modern revivals of the show aimed at people who liked it as children and have now grown up -- notably Mazinkaiser (opening) and Shin Mazinger Z (opening).