(As with my earlier review of Wonder Woman 1984, this is an immediate response having just finished watching the film. There won't be a follow up long-form review however, as that would mean having to watch it again)
'Tenet' is Nolan's least enjoyable film by some distance. A two and a half hour festival of incomprehensible exposition, smugly in love with its own deliberately convoluted cleverness.
I've got no issue with a film dropping me into an unfamiliar setting and expecting me to orient myself. That's part of the fun of watching well written and smartly plotted movies. However...when we're in the final scenes of the film, and I'm still not sure what is at stake, what certain characters are doing, and what any of it means, then I'm sorry I'm sorry...but that is a failure of storytelling.
A film which becomes richer, deeper, and more meaningful with repeated viewings is a beautiful thing. But you should NEVER have to watch one multiple times in order to comprehend it in the first place.