Unsettling. I felt creeped out and uncomfortable after watching this.
I'm Thinking of Ending Things is very heady; the kind of movie you have to watch a bunch of times or read a lot about to understand. You can tell something is off, but won't really know what's going on while you're watching it (you might be able to guess a bit if you're used to these types of movies). It's confusing. Slow but intriguing. It was like watching a weird dream - you know it means something but can't quite tell what at first glance and have to dig deeper.
I can definitely see how people would find this boring because not much actually happens. I kept watching to try to make some sense of it, hoping for an answer. It's strange and surreal. Weird. Disturbing. It'll stick with you in a really uncomfortable way, kind of like a bizarre nightmare that clings to you for the whole day or week.
I'm giving it 4 stars because, even though I didn't really get it at first (still not sure I do) and was a little annoyed after finishing it, the movie stuck with me and made me think. It was successful in making me uncomfortable (I just can't use that word enough for this movie), which I believe was the intent.
Watch this if you want to dig into the murkiness of the human psyche and don't mind interpreting a movie on your own/with the internet. Skip it if you're looking for casual viewing or like things wrapped up neatly.