This doesn't take into account differences in personal preferences, as it doesn't know what movies I prefer, and so can't compare my preferences to other people

This doesn't take into account differences in personal preferences, as it doesn't know what movies I prefer, and so can't compare my preferences to other people's. Not everyone has the same tastes, and personal preferences matter. You could improve your system's recommendations by combining your approach with a collaborative filtering algorithm. Mine's very accurate on small data sets, and a detailed description of it can be found here: fmjlang.co.uk/morse/MORSE.html