My aunt, uncle and cousin have lived in Nigeria for 14 years (they actually met in Nigeria)
They live in Jos, which is kind of in the middle - the interface between the Muslim north and Christian south. There have been times when we’ve worried for them, such as 2 years OK, when there was widespread religious rioting in their area, but mostly not.
They live in a guarded compound, and keep a guard dog for security. Travelling in the country side is less safe, but not outrageously so (e.g. my aunt drives an hour or so alone once a week to a hospital a bit out of the way (she’s a doctor)).
My cousin has lived there since he was 2, and is a relatively normal kid (well, as much as any 16 year old is). He’s had a good education via correspondence and the American boarding school in Jos (he’s a day boy). He has both expat friends and Nigerian friends (the school is about 50-50 expat-local)
We can’t send them anything other than paper letters in the mail (no books or gifts), because it will get stolen.
But overall, they seem to live a pretty normal life, and have a number of expat friends.
They are planning to return to Australia soon-ish so that my cousin can finish his schooling and prepare for university. But they love it, and to them it’s home.
Health-wise, they do get typhoid and malaria on a semi-regular basis (a few times a year), but they manage it with various medications, and it doesn’t worry them too much. I guess my aunt being a doctor it’s hard to say what they think of the hospitals etc. since they take care of themselves mostly.
Infrastructure is not quite what you’re used to, when they first went, they would have daily power outages, but it seems pretty reliable now, they have a reasonable mobile phone network etc, although calling Nigeria from Australia (or vice versa) is still brutally expensive. They don’t have broadband, but I don’t know if it’s because they can’t get it, or don’t think they need it (my aunt & uncle not being the most technical people in the world). They use dial-up for email.
Based on all they’ve told us (they send emails once a fortnight) I would love to go and visit them and spend time with them, but I don’t think living in Nigeria long term would be for me.