Unfortunately Fermat's Room adds nothing new to the idea of trapping a group of people in a single room and having them slowly piece together how they know one another. The general premise of course sounds interesting (at least to me) a shrinking room and four mathematicians must solve their way out. But the problem begins right there, they are only given one minute per question, which makes it damn near impossible for the audience to keep up. Not to mention when they begin to work out the problems on the chalkboard, the camera hardly ever puts it in frame, which would have been great for the audience to kind of sole the problem along with the characters.
But instead the movie shifts focus away from the riddles/enigmas and focuses on them trying to figure out who has put them there and why. This is where Fermat's Room becomes derivative and generic, this is very familiar territory for this type of movie and it is spun in an unengaging way. I personally would have enjoyed focuses more on the enigmas and trying to include the audience more (possibly by giving the characters more time to solve them).
And the unfortunate aspect of the movie is the Spanish subtitles, they were very fast moving which didn't help things (Just something that was unavoidable sadly). Like when the characters are dissecting the enigmas, the lines of dialogue moved too quickly to follow along with how they were solving the problem.
But when all is said and done, Fermat's Room is an interesting, little thriller that has just enough distinction from other films in the genre to make it worth mentioning.