Note, there will be spoilers for previous MCU films, but I'll try to save Black Widow-specific spoilers for the footnotes.
Let's get this out of the way - Yes, it's weird that they waited until after the character died to give her a solo movie. Yes, the movie feels like an apology to Black Widow fans for not making the most of her character before killing her off. And yes, all of this makes it difficult to judge the movie on its own merits. But give me a break.
In a world where people have fantastic powers and supernatural abilities, it's a little weird to watch a movie about (mostly) unpowered people. It's like watching a Star Wars movie that doesn't center on Jedi. But Rogue One (and even Solo) proved that such a thing does work, and so does Black Widow.
So, a quick, "spoiler light" summary. After Civil War, Natasha Romanoff is on the run from the US government. She finds out that the assassin organization that trained her is still in business, and decides to shut it down for good. She teams up with her former family, and faces off against an enemy who can mimic her fight patterns. The plot is actually pretty light.
Thematically, Black Widow reminds me more of "Captain America: The Winter Soldier" than any other MCU film. Taskmaster is very similar to the Winter Soldier (see "spoiler 1" footnote), both movies involve a hero bringing down an organization they used to work for (spoiler 2), and they even both have similar climaxes (spoiler 3). But overall, both movies just feel more like spy films than superhero films.
I don't like spy films. I'm not a huge fan of The Winter Soldier, because it reminds me too much of the Bourne movies (which I pretty much despise). But somehow, Black Widow works for me. Maybe it's just because I prefer having a female protagonist. Maybe it's because it's newer. I do tend to like brand new MCU movies more than ones I've seen a lot, so who knows if Black Widow will age well.
Every once in a while it struck me that Natasha wasn't in any real danger, because we already know how she's going to die. But that really didn't make the action scenes any less intense. I tend to rewatch MCU movies a lot, so most of the time I already know the main character isn't going to die. Hell, the first Captain America movie was told mostly in flashback, and we still didn't find it any less exciting knowing he wasn't going to die.
One thing that annoyed me: While the majority of the Black Widow takes place between Civil War and Infinity War, the post-credits scene takes place in the current time, which leads me to a bit of a Star Wars-esque conundrum. In the future, should new MCU viewers watch Black Widow in timeline order or film order? The movie works better if you watch it sometime before Infinity War, but then the post-credits scene goes and spoils her death in Endgame.
Bottom line: Black Widow isn't bad. The action scenes are top notch. The plot is pretty basic. It's a little too similar to The Winter Soldier. I can't quite rank it in the top 10 MCU movies, but it's close. It's not going to blow your socks off, but it's a worthy addition to the series.
Spoiler Footnotes:
1. They're even both mind controlled.
2. Hydra-infested SHIELD vs the Red Room.
3. In that they both involve fighting on an air vehicle while it crashes to the ground.
