To say it clearly, "Ex Machina" is much better than "Her". A young software coder gets a one-week appointment in a remote research facility in a mountain forrest to execute a turing test. His employer, a billionaire genius, had created "Ava", a smart robot with a female body and wants to know if this android is really an AI. "Ava" will pass the test if her interviewer cannot distinguish her behavior from human (this is a spoiler-free blog. If you want a synopsys you can find it here wikipedia).
"Ex Machine" is set in a near & plausible future. The only science fiction issues (not yet available technologies) are the AI and her humanoid body. Director Alex Garland, who also wrote the script, created a fascinating psychological triangle between the young and smart coder, who is eager to fulfill his job, the employer, a bully with a sharp mind, and the sexual highly attractive machine-girl ("sex machina"?). This creates tensions and conflicts which escalate and get more and more dramatic. The plot is spiced with intelligent dialogues and philosophical debates about evolution, creating life, freedom of will, sexual attraction, deceit, survival strategies and much more. Even that the plot was highly intellectual it had a lot of suspense and I really cared about the fate of "Ava" and the humans.
"Ex Machina" benefitted from the fine cast. Domhnall Gleeson, as the coder, Oscar Isaac, the controlling boss and the stunning Alicia Vikander, as the smart & alluring female machine, did great jobs. Director Garland, cinematographer Rob Hardy and their team created a cool and stylish scenario (the research facility looked a bit a like a gallery for contemporary art) immersed in a gorgeous and wild mountain environment. Part of the fun is the soundtrack, mostly created by members of the group Portishead.
"Ex Machina" is the proof that a science fiction film can be smart, entertaining and stylish at once - the best movie of the year so far.