Amazing. Such a unique, yet necessary plot and cast of characters. Major themes include:

Race beyond the American scope: A main premise of the book is Ifemelu's move from Nigeria to America, and needing to wade through the meaning of "race", something that does not exist in an almost all Black country. The word "black" was foreign to Ifem as she is just "African"!
The idea of race was also explored by comparing and contrasting the UK and US: a favorite line of the book is "in the UK Black and White people work together but don't play together; in the US Black and White people play together but don't work together."
Finally, when Ifemelu moved back to Nigeria, she hadn't realized how much she had internalized the idea of race, and almost reveled in her newfound "privilege" as upper caste to make up for her lack of standing in the US.

Ifemelu's blog posts were a great supplement to this premise, and aided in the reader's understanding of her experience. It also gave the reader an opportunity to hear Ifemelu's reflections on microaggressions, negative encounters with friends, etc. despite the third-person narrator.

Home, and the place 'in between': Ifemelu rediscovers the meaning of 'home', with moving to the US being difficult, but then moving back to Nigeria also feeling difficult. The idea of home is represented as something as tricky as it is in real life; as something that can feel lost and perhaps never found the same again.

Microaggressions: Ifem and Obinze are surrounded by several well-meaning people who often say some problematic things. Both characters are very gracious, yet it is fascinating to see these instances from the receiving end. Small comments that may not see serious to those who experience them once, don't understand the harm of undergoing several a day, particularly coming from those you trust and are close to.

Immigration & deportation: The contrast of Ifem and Obinze's situations was done really well– we were offered the stories at similar times to make the timeline make sense, yet they were still separate enough that we could give each one its required attention. Ifem's story made use of a narrative of using who you know to get ahead (and even the benefits of "getting in" with WASPs early on, despite it feeling beneath you), and particularly using relationships to get ahead.
Obinze's story represented the solitude of immigration– trying to get by all on your own (despite trying to lean on those around you) and how little it will get you. He also personified more of the day-to-day struggles of having a visa with no work allowance, the anxiety of using someone else's identity, and reckoning with deportation (and how it feels disappointing, but also is a bit of a relief).

Adichie's writing was so great. It read like a narrative yet had so much nuance sprinkled in I felt like I learned so much from it. The issue of race was never too heavy-handed or forced, yet it was still a very impactful underlying purpose to the story. I didn't love the ending and felt like the reunion of Ifem and Obinze was a bit rushed, yet still feel like the story was wrapped up.