I finally also watched Tenet yesterday. I was actually surprised about how it turned out to be - in good and bad ways.
On the positive side, the story made much more sense than I expected. It helped that I watched with my wife, who is awesome at this kind of logical puzzles. Together, we figured it out pretty much completely - even if some loose ends and paradoxes remain at the end. But that's intentional I'm sure, and Nolan has said he didn't aim for scientific accuracy. (My main gripe: how can the protagonist lead the mission by having set it up from the future, if he only can know about the situation because he was involved in it? I suppose that's a typical sort of problem with time travel plots though.) Also, I thought the music was much better than I anticipated. After reading all about the music overpowering dialogues (which doesn't bother me anyway, with closed captioning), I expect another piece of Zimmer-like bombast. But the soundtrack is actually often quite subtle, or even largely absent from some action scenes, and fairly abstract in places as well (by using reversed sounds etc.). Quite strong. I also liked how the film 'felt' real in most places, probably because it actually includes relatively few vfx shots (as I read afterwards). The inverted fighting also worked pretty well, even if it was hard to follow sometimes. (And apparently also actually filmed that way!)
On the negative side, I thought there were actually quite a few clumsy bits in the film. Usually, you can at least expect good filmcraft from Nolan, but I thought it wasn't so good here. There were a couple of jarring or pointless cuts (e.g., before his first meeting with Kat, you have a five-second shot of the protagonist entering a building lobby and greeting someone at a desk - and instantly we switch to him entering a room where Kat is; or, later on, a brief scene where Sator is given binoculars on his yacht without much point). The pacing was weird as well. Several action scenes felt really quite slow and boring (especially the Tallinn car chase), there were long talk scenes that felt fairly irrelevant and, again, boring (I guess because I thought the characters and overall plot fairly uninteresting), and the action in general tended to be either underwhelming or chaotic (I had no idea what was going on in most of the final battle scene). Also, some of those lines you'd expect to presage events are actually empty talk (e.g., 'tenet can open doors, some good, some bad' - but the password is used only twice and both times to the advantage of the protagonist).
On the predictable side (for a Nolan film), of course women have few and pretty lame roles and there is virtually no humor or levity anywhere (I even read that the protagonist's one funny line ('Where's my hot sauce?') was improvised by Washington) - which would be OK if this was actually a profound or serious drama, but it really isn't, which makes some of the supposedly cryptic or profound lines (especially in the first half hour) appear pretty silly.
As a whole, I can't say I was bored or underwhelmed (even if half the final third is quite predictable once you've figured out the plot - like that it's the protagonist at that Norwegian freeport and Kat diving from that boat), but I also wasn't very impressed. Ultimately, I guess this was a lot like Nolan's Batman 1 and 3, Inception, and Interstellar for me: good in places, poor in others, and rather unengaging and 'meh' overall.
5/10 or 6/10 - can't decide.