The biggest difference is going to be the College system, you apply to a College within the University. This is where you're going to be living, this is where you're going to be socializing, where you're going to be eating, where most of your time is going to be spent. While lectures and labs are going to be University wide, Tutorials, Supervisions and Seminars, are going to be College wide.
This means that not every College can offer, every single course, and there may be only one or two other people, at your college doing the same course as you. You can expect these Tutorials, these Supervisions to be very intense and very small. I've gone through all of the College's, at Oxford and Cambridge, and listed later in this chapter which courses they offer, at which College.
The timings and workload at Oxford and Cambridge, is going to be very different to other Universities. You can expect to be working weekends, you can expect the workload to be very high. However, you're only going to be at University, for three-terms and these three-terms are only, eight or nine weeks long. That's less than 30 weeks at University, across the whole year. So you have a lot of time to relax over those holidays.
While other Universities will have large lectures, Oxford and Cambridge do a lot of their teaching, in Tutorials or Supervisions. Due to the small size of the College's, these can often be one-on-one with some of the world's, leading academics. These happen on a daily or a weekly basis, and these can be quite intense, because if you don't know what you're talking about, you're really quite stuck and exposed.
Due to age of Oxford and Cambridge, some of the Colleges are very traditional, and very formal. Some of the newer ones are much more relaxed, but some of the older ones still insist that you wear gowns, to formal dinners which can happen weekly. These are sit-down, served three-course meals, where you're expected to go, and observe excellent etiquette the entire time. If this isn't your thing, then maybe you should look at a different University, or look at some of the more modern College's.
The last difference you need to know, about Oxford and Cambridge, is that you can only apply to one. You can only apply to Oxford or Cambridge, you cannot apply to both. And the deadline for applications is earlier, than the normal UK deadline, you have to apply by the 15th of October. Picking clothes is almost as hard as picking a University, because you need to find somewhere, that you're going to fit in, and somewhere you're going to be happy, for the next three or four years of your life.