My theory is that people who found No Country boring are only familiar with straight forward plots. It takes thoughtfulness to enjoy the film, and the people I know who disliked it lack that.
The movie doesn't hold your hand. John Wick requires lots flashy action because the average viewer would benefit from a close caption that says "feel excited now," while No Country is boring unless you're brain is actively participating.
I don't really think it's accurate. I love when the main plot is deeper than just what you can see. I just watched The Green Knight and I was constantly trying to find the deeper meaning to whatever was happening and how it related to the overall plot in a more symbolic way.
My favorite movies are Pulp Fiction and The Fifth Element which both have multiple storylines. Although for The Fifth Element, the overall plot is straightforward.
I just didn't find this movie interesting and the "intense" scenes didn't really land for me.
It's probably been 17 years since I saw it, and I didn't love it. So my memory on it isn't the best. So I'm going to give the obvious example of the coin scene. Which from what I remember commanded some gravitas.
First intense scene like that comes to mind is the opening to Inglourious Basterds. I'll let you know if I think of one I like more than that. But that's probably it.