Oppenheimer is well worth three hours of your life. It's impressively paced, keeping one's attention without fights, car chases, or explosions. OK that last isn't wholly true, of course.
The theater was almost completely full, while it's been nearly empty for most movies I've seen recently (which isn't that many). It's good to see that a long serious movie that frankly has limited suspense (because you know at least most of the story already) can still draw a crowd.
The only problem I had was that my bladder couldn't make it all the way to the finish line, so I missed a couple of minutes midway through the film.