Agreed. Too many apple-to-orange comparisons. But categorizing by genres will require some amount of work. How about having an option "can't compare"? That

Agreed. Too many apple-to-orange comparisons. But categorizing by genres will require some amount of work. How about having an option "can't compare"? That the user can indicate they saw both but cannot compare. With enough data, maybe you can cluster more frequently compared movies together or even making categories automatically? (Downside is more complex UI; it's better to keep UI simple, so I'm not sure).