Ex Machina caught my eye because it's science fiction and has a focus on artificial intelligence. It's also a psychological thriller, which isn't my favorite film genre. After watching, I'd say it's much more about the mind-games genre than it is about the science fiction aspect, but both are well executed.
I enjoyed this early part, with all the introductions and bits of background revelation. It certainly helped that I empathize with Caleb's character: smart technology guy, somewhat isolated socially, excited about the idea of artificial intelligence. The setting was also interesting, with the juxtaposition of a high-tech facility buried way out in the wilderness. And of course there was Ava herself. There's a good amount of build-up before you see her for the first time, which adds a sense of mystery, and the effects they used to create a see-through android body are pretty neat.
Once the players are all in place, the rest of the movie is about mind games played by the various parties on one another. Everything boils down to Ava wanting to survive and be free. It was mildly interesting to see how it all turned out, of course, but I found the resolution and reveal portion of the movie less interesting than the initial setup. That's just my personal bias, of course - I like the speculative fiction aspect more than the mind games.
Ex Machina poses an interesting scenario, and the movie is put together nicely, especially considering the relatively low budget. I've seen many worse movies that cost a lot more! The psychological thriller aspect isn't really my thing, but it seemed to be well executed. In the end, I'm glad to have spent a couple of hours to watch it.