Tenet is complicated and captivating in its presentation. The story itself combines international espionage with something that feels like inception (except with time instead of dreams). The secret to what is happening lies within the name. Imagine if you will a time-bending 007 and you might come close to grasping what is happening here, the problems, however, lie within its presentation. You'll have to really pay attention to the little details to follow exactly what is happening.
This all centers around a singular mission and that mission involves multiple pieces from different characters and story directions that all bring it together. With all of the pieces involved, it becomes more than a little bit confusing. The more you watch it (repeat), the clearer it becomes but there will be those who will have had enough after once. Those who want to watch/rewatch it will find more and more to understand what is happening. It's a breakthrough idea that was done in a way that has never been done before.
Is it ahead of its time or simply out of time... That's up to you.