I will preface this by saying that I haven't read it again in over a decade, but I remember mostly liking it on my second read. I switched schools mid high school, so I had to read it twice for school. I didn't like it the first time, I think I was too young and not interested in interrogating it much the first time I read it, but enjoyed on the second reading.
As you mentioned, it did try to portray precolonization Igbo culture as Achebe understood it. And I thought that it was a brave choice to focus on a lot of flaws and issues with precolonization society, where many characters are some shade of moral grey. Though this does lead some people to think for the same reason that it downplays or softens the problems of colonization, despite that being the titular "things fall apart", but I obviously feel that wasn't what Achebe intended. I think that Achebe was trying to portray the motivation for the various downtrodden and Nwoye to go along with Christianity and colonization.
I wish we had more portrayals of precolonization societies in literature.