Greatest in what way?
Be careful in your definition of serial this is more specifically a mini-series. It was 11 episodes and 17 hours long and was supposed to be a one time event.
I think that this is a different creature than something like "The Sopranos" which rain for like 8 years and in my mind is the most iconic of all television series (said the American who did not really like it).
Also keep in mind that Heimat was made in response to the 1978 mini-series "Holocaust." Most would argue that Holocaust was a much more "significant" mini-series.

Fassbinder's 'Berlin Alexanderplatz' and Edgar Reitz's 'Heimat' (1984) are among the best tv series ever, in my opinion. I'll be happy to watch them again and again.
-I don't discriminate between entertainment
and arthouse. A film is a goddam film.-

Absolutely excellent on all counts!

I cannot see it being surpassed ever, anywhere. Equalled, maybe. Surpassed, no. It is one of the most sublime feats ever to be committed to film.
I saw it when it was broadcast originally, and then again some years later, and it has left a deep impression on me, especially since I was born in Germany. Everyone I spoke to, who had seen it was compl etely blown away by it.
I only wish that I could give it 11 just so that it would stand out as, indeed, it deserves to