That the Reapers are essentially giant parasites, sequestrating other species genes and co-opting them for their own purposes - like the Borg in Star Trek, presumably indoctrinating them on the way.
That the Protheans couldn't be adapted, placing a limitation on Reaper technology.
That the Reapers appear to have reached an evolutionary dead-end, being unchanged in millions of years.
That each Reaper inside its' flying machine likely looks like the species it is derived from.
That just about every species we see in one way or another has tendencies towards genetic superiority that is exactly like the Reapers.
That they think of themselves as ideas rather than as persons.
That the Protheans' fate was even worse than we first surmised.
That something cleverer than all-out war will be needed to defeat the Reapers.
That, numbering in their thousands, and being the consequence of Reapings, the Reaper species itself in every way sums the past history of the galaxy, and that the war to come is very much between the past and the future - but that the future itself looks as if it could be just another Reaper civilisation.