Translation:The cafeteria food is not good.
"Food" can be singular or plural. If you're talking generally, then it should be plural!
'The food at the cafeteria is not good' should be accepted as well. With 'in' it kinda sounds to me like it would have to be eaten on the spot. But if I grab a take-away sandwich and then complain about it while sitting in the classroom, I will use 'at', not 'in'.