I don't know if the whole thing done on a computer screen is necessarily bad. I like Fail-Safe (1964), even though most of the suspense is done over phones in that movie.
However, everytime someone says a horror movie is really good, I always find it to be nothing more than decent, to horrible. The last really good one I saw was The Skin I Live In (if that counts), and The Descent. But it's really hard for horror filmmakers to put out a product that good, in my opinion. I was disappointed in It Follows as well, but at least it was okay/decent, as oppose to horrible. It's just not the masterpiece people are making it out to be.