Some subjects are harder to get in for than others, but it is impossible to generalise.
The courses in Cambridge tend to be more traditional and academic than in other universities, but at the same time manage to embrace the latest research and state of the art technology. They form an excellent basis for your future career. Be sure you know what your course involves before you decide to apply for it. Alternatively you can contact individual departments for departmental brochures or make inquiries about courses at College Admissions Offices. If you come to Cambridge for an open day, ask to talk to a current student about the course you are interested in - even if you just get a contact address, it's worth it, because they can give you a real insight into the course.