I have heard of this is us. I have not seen it yet, but I have seen the trailer. I don't know if I will watch it or not, but it certainly looks interesting and it looks like it has been well made. It will likely have a good clean base and catch on.
I have not heard of the show "This Is Us" and wonder if it is that good as to have NBC request 18 episodes. My guess based on the shows title is that it is either a show based on a family or a ethnic group and highlights facets of their way of life.
I have not previously heard of "This is Us" because I do not generally watch cable TV programs. I did a quick google search and I can surmise that, based on just the cover alone, this would not be a show I'd be into. Who gives a crap about a bunch of people's fake lives when I have too many things to do with my own? Additionally, I'm super against overweight/obese normalization, so I really dislike that one of the "couples" featured has a fat woman and I would never watch such contrite drivel.
No, I have not heard of this show because so many new shows come out every season. Most shows on the major networks fail within or immediately after the first season. Most people today will wait until a show gets good reviews and will then watch it later online or on Netflix.