Fun but frustrating is a really good description for Tenet. I was pleasantly surprised how "simple" the story is for the most part. At its core, it's a pretty standard spy film, complete with an over-the-top Russian villain, a heist sequence, and plenty of twists and turns in the plot. The action is really well filmed and edited here (something which I feel has been a struggle for Nolan in the past), and I was pleasantly surprised the film wasn't as deadly serious as I was worried it would be. John David Washington really brings something here as a protagonist who is in slightly over his head.
It seems I have the same complaints about the sound mix as most everyone else: it almost feels like Nolan is challenging the audience to make out dialogue at times. I basically gave up trying to understand anything during the rail yard and sailing scenes, for instance. I also found the opening scene almost punishingly loud (I didn't even see it in a plus-format), but I do think I "adjusted" to the audio a bit as the movie went along. The score is, of course, tense and awesome.
After all was said and done, I felt like I understood the broad strokes of the story, while perhaps missing out on some details. I can completely understand why that would be frustrating for a lot of people, but I had a lot of fun just watching it as a spy movie where the plot is perhaps a little muddy and confusing.