"Oh my God...that's it? They don't even catch him? That's the ending?"
I'm with you, Mr. Movie Opinionheimer. I thought we were watching "Lethal Weapon 6," too. You did seem quite serious in your critique, as the screen shows you clearly who wrote and directed the movie.
"Didn't the Coen brothers direct that funny Dumb and Dumber movie?" I can imagine you asking your wife in the car. It's a common mistake, but no--you're getting hung up on the brothers part.
"Why couldn't they just have had the sheriff shoot him when he was hiding behind the doorway?" You'll ask a few days later, as your terribly loud breathing--which you had during the entirety of our shared time together--begins to sound more labored with the strain of the movie's ending weighing heavy on your heart (and lungs and other breathing parts).
"Was it supposed to be a complex conclusion, not necessarily about the resolution, but more about the chase--and the realizations arrived at in that time?" You'll propose, after you see it win several awards over the winter months to come.
I can actually answer that last one: No--there's actually a sequel planned. There will be more money on the line, and a more satisfactory ending meant to give your mind peace.