Ex Machina is essentially a philosophical thriller that examines the state of mind of the characters in the story — all three of them.
The acting is superb, and it has to be. What the characters say through their expressions is just as important as what they say audibly. A great deal of credit has to be given to the first time director Alex Garland — who also wrote the screen play for this movie as well as 28 Days Later and Sunshine.
This is science fiction done right. My only beef with the movie is the ending. I might have gone a different way, but the ending they gave it is satisfactory.