tl;dr Not the Liam Neeson you expected.
The setting is familiar. An aging, frontier-living, American unwillingly gets pitted against the Mexican cartels.
Arnold Schwarzenegger did it on The Last Stand (2013).
Sylvester Stallone did it on Rambo: Last Blood (2019).
And in 2021, it's Liam Neeson.
But what you get, is not what you expect when you think of mexican cartels vs Liam Neeson. As the story progresses, there are many moments when you think the action is about to kick-off to something along the lines of Taken, but it never does. The Marksman constantly tries to be more like a drama, and less like an action film, and it fails on both. The action sequences are good, but few and not over-the-top as we have come to expect from a Neeson movie. And the drama is sub-par.
Go ahead and watch it, if you don't have anything better to do...