Mortensen, who portrayed heroic Aragorn in the three Lord of the Rings films, fears "geek" Jackson allowed special effects and technology to take over the series after making a great first movie.
In a candid interview with Britain's Daily Telegraph, he states, "Once he (Jackson) had the means to do it, and the evolution of the technology really took off, he never looked back. In the first movie... there's sort of an organic quality to it, actors acting with each other, and real landscapes; it's grittier.
"The second movie already started ballooning, for my taste, and then, by the third one, there were a lot of special effects. It was grandiose, and all that, but whatever was subtle in the first movie gradually got lost in the second and third."
He can see similar issues in The Hobbit films, adding, "It's like that to the power of 10."