I read them all. I think I liked the first book fine, it's more of a self-contained mystery, which might be better. The aliens are probably most prominent in the second trillogy; there's loads of them and I quite like the Commons of Jijo.

I feel like the series is sort of missing pieces? Like, across the five books it is in, WTF was going on with Streaker's discovery is never really explained, the whole the-galactics-aren't-being-honest-with-us thread is never satisfyingly resolved in the whole series, and at several points in the chronology it feels like there could have been a whole book about the stuff that happened since the last book.

The whole series is An Aesop on how science is good. Which is fine, doing science is good and you can spend a series reminding people of that if you would like. But it's strange to find that as the point of a series that otherwise seems to have all these frankly conservative ideas about colonizing space planets and about some people being just inherently more or less "uplifted" than others. Uplift seems to stand in for a person's moral value without what I would consider sufficient critique. Like, paternalism is bad when the galactics do it, but when humans just have full power over a dolphin person's entire life that's fine somehow, you need it to do Uplift, the thing the books are about. The whole Uplift concept has unavoidable parallels to European notions of "civilizing" people by using military force to make them act more like Europeans, which I don't think are fully examined.

I also remember them as having weird 1980s gender ideas in them, like the men are normal and the women are viewed through some weird filter and the other gender humans are entirely absent.

I think there are more interesting books to read about the structure of minds and the diversity of subjective experience. For example, Diaspora only comes out a year after Heaven's Reach, and also has all sorts of weird aliens, but it additionally has defensible gender politics and a much more cogent thesis on autonomy and what the powers of science may or must be used to do. Or, A Half-Built Garden is all about what happens when galactic society arrives to save the humans, and the humans maybe finally don't need saving.