I don't know as much about this period of history -- the very early years of the 20th century -- as I do about other eras. This is partly because in Louisiana, where I was schooled, history classes always stopped at the Civil War; and partly because when I went to the university (at least the university I went to) you could take either US or World History, and I went for World.
What little I knew, I had gleaned from reading novels written during the era -- Sinclair Lewis, for example, or Steinbeck -- all of which only referred obliquely to the political situations. I had picked up a little more from reading political blogs, and doing research when I taught my American Epics class, which required me to know the contemporary historical background of Grapes of Wrath, among other texts.
This series is excellent for correcting my ignorance, and might be equally excellent even if I had known more. For one thing, I had never paid much attention to Teddy Roosevelt, since he was a little before the time of the novels I was teaching. Burns' documentary is really good on explaining the scope and breadth of TR's work, as well as his influence on FDR.
It's also really good on explaining the influence of Eleanor Roosevelt on her husband. The parts about their relationship, and Eleanor's own character, are also great.
The vast intertwined relationship between the two branches of the Roosevelt family was something I knew nothing about. That part was very enlightening.
Also, I knew FDR had polio -- but not the extent of how the disease changed and shaped his life. He was our first, and I guess so far our only, disabled President. I'd never thought about that or seen it expressed. Disabled erasure!
Also, of big interest to me, both TR and FDR's attitudes and work with the labor movement. And Eleanor's work with the movement, and with the dispossessed during the Depression, as well as her work with groups of nascent women voters. (There's also a sizable hint that maybe Eleanor was bisexual. Though I might be reading too much into that part!)
Anyway! It's a long series, as I note above -- almost 14 hours, and served up in big chunks -- but it's really well done.