It was only a matter of time before Christopher Nolan would do a real time travel flick. He's the king of modern blockbusters and a real sucker for twisty/serious narratives. Tenet is pretty much what I expected it to be, including all the things I don't like about Nolan's films. But coming from him, it's certainly not his worst.
A secret agent is recruited to prevent a third world war. While he presumes a nuclear threat, our world is actually under attack from the future. They devised a way to give objects negative entropy, effectively letting them go backwards in time. A fun plot device that runs through the remainder of the film.
Nolan is oldskool. It's probably why he's generally revered, but for a contemporary blockbuster director I don't think it's a plus. The action scenes look rather dull, the score feels outdated, the pompous and convoluted story telling slows things down and Tenet doesn't do anything spectacular with the time travel element. Just a mediocre blockbuster, at least the pacing was a better better compared to his other work.