It's difficult to speak about this film without ruining a great deal of the plot so if it sounds like I am being vague just know that it is intentional. I will say this though, if you want to even have a chance at enjoying this film beyond the very Christopher Nolan effects and music of it all, you are going to need to pay very special attention to what is going on and maybe even back the film up a bit to repeat certain sections.
This is one of the more convoluted films I have seen in a long time and I think the fact that it is really difficult to understand what is actually happening is part of the reason why the critical response for this movie has been a bit less than stellar or at least a bit worse than you would expect from Nolan's work.
Just like basically everything that Nolan does, this movie cost an absolute fortune to make at over $200 million. While it wasn't a financial bomb or anything, the fact that the official figures put the take on this film at $360 million or show might simply be a "break even point for it." Movies of this magnitude normally have massive marketing budgets so a decent rule of thumb is that they need to double the production cost before it is considered a financial success.
As far as the plot is concerned I want to be as vague as possible because the story is actually pretty good if you enjoy science fiction stories. It is science fiction only in the technology that it involves, not the time period and in many ways that sort of sci-fi appeals to me a great deal more than space stations and alien shooting lasers and one another.
Basically in this movie there is a threat to humanity by villains involving technology that can invert time and all reality. The importance of this and how it works is extremely difficult to follow given that it is such a difficult concept to convey using words. We are treated to some really unusual and interesting special effects though and I suspect that this is a big part of the reason why the film's budget was so high.
The visuals can be quite dazzling because of the fact that since a central theme of the entire thing is inverting time, there are scenes where all but a few of the people in it will be moving in reverse. I can't even imagine how something like this was filmed but it is really cool to see. So therefore even if you don't "get" the story, these visuals make the film worth seeing on their own.
I also quite enjoyed seeing Robert Pattinson in a film that isn't some sort of tween Vampire film for once. Even though he made a fortune on those movies I think being in them probably damaged the longevity of his career in a lifelong sense.
To give you an idea about how potentially perplexing this film can be to many, if not most viewers, I found an interview with Pattinson where he hilariously stated that there were "months at a time while filming Tenet that he wasn't even vaguely understanding the plot of the movie."
I don't know if it was originally intended for this movie to be as confusing as it is or if they got $100 million in and though "fuck it, we have to finish this thing and people are going to go see it because of Nolan's name anyway."
Should I watch it?
I think that only under very specific situations should you even attempt this film. It is seriously confusing but then again, maybe I am just not very smart. This definitely isn't something that you can just kind of pay attention to and have any idea what is going on. In my mind this is something that requires your undivided attention and if you are into that sort of thing you are going to enjoy this one and perhaps you will end up like me and still have a lot of unanswered questions at the end. I enjoy when films can have a half-conclusion but still leave you thinking about it after it is all over, and this is one of those movies.
That being said this film might be a bit too perplexing to some people, particularly if English is not their primary language.