I rushed to see Black Panther before it disappeared in the explosion of Infinity Wars. I believe I was the last white man in America to see it, judging that I was the only white man in the theater. Then again, I was the only man in the theater, period. The sample size was rather small--I think there were three of us watching, in total.
In any case, I quickly realized this wasn't a "regular" Marvel movie. It was a Marvel character, but it didn't quite have the comic book feel. It had more of a James Bond feel, to be honest. The villains, the set-piece scenes, the chases, were all very Bond-ish. There was even a Wakanda version of "Q."
But it was more than Bond: The more I thought about it, the more I believed that the movie is a remake of The Lion King. So I did what everyone does when they feel they have an original idea. I googled it. I'm not the only one who believes this. See the video at the top (mild spoilers).
And these links (these likely have mild to massive spoilers, click at your own risk):
Here's one spoiler: nobody broke into song in Black Panther. Actually that's a lie--one character did break into song, but not an original song, and not sung well.
I said all that to say this: This white man will now explain why Black Panther is so popular.
It's popular because it's earth-bound and possible. It's possible that an exclusive black, blood-line-ruled nation could rise up with technology beyond the entire world to right the social justice wrongs of the "colonizers" (yes, a white man was called this in Black Panther). It's possible that a nation can show everyone what it's like for people to live together in peace and harmony. It's possible that black people don't have to kill each other.
These are deep themes. The movie hits you over the head with them, but in a rather enjoyable way.
Black Panther is so popular because it's a movie women like, more than it's a movie for non-whites. It's not the typical Marvel movie. In fact, you don't need to see any other Marvel movie to "get" it. My guess is you will want to see it if you're a Marvel movie (or MCU) fan because Disney will be mining this for years.
By the way, Disney is run by white dudes like me. I think they were just as surprised that it turned into a blockbuster. Which is why it's still in theaters the day Infinity Wars came out.
Circle of life to y'all, and I'm out here, so discuss amongst yourselves.