I graduated from Cambridge a couple of years ago, but I'll have a go at answering this. As you say, it's variable. The exact number of essays per week varies from supervisor to supervisor, and therefore varies between colleges. However, it's certainly not unusual for each of the main subjects to be setting 1 essay per week; therefore, that will usually be 1 essay each in anatomy, physiology and biochemistry per week in the first year, and 1 essay each in pharmacology, pathology and neuro/behaviour in the second year. The second year will probably have a few endo/reproduction essays thrown in too, but they may not be every week, depending on the supervisor. These essays aren't usually huge though, a couple of thousand words is usually more than sufficient, so you get used to bashing them out in a few hours. There are a couple of other minor subjects in first year, medical sociology and statistics, but they are pretty trivial and many colleges will only have a couple of supervisions for them. In terms of contact hours, first and second year will see you occupied with either lectures or labs for most working hours between 9-5, but some days there will be a few hour or two gaps here and there.
In terms of exams, of course they aren't easy, but they are manageable and the majority pass second MB well enough. The general consensus is that the 2nd year is probably the hardest, followed by 1st year and 5th year (but 5th year is now easier than it was, probably). If you keep up with the work thorughout the year, and set aside a few weeks for revision, it's all perfectly doable though, as evidenced by the fact that most get through first time, and most of the rest get through the resit. I don't know how the exams compare to other medical schools as I didn't go to them, but I can't imagine it's easy anywhere really. I certainly never regretted choosing Cambridge, and most people manage to have a decent social life outside of their medical studies! The 8 week terms of undergrad are relatively intense, but 8 weeks is a pretty short time, and you therefore end up getting pretty much half the year off for the first couple of years. A bit of work in the holidays will be necessary, but not too much in my experience.
Clinical school is different again; your holidays are much shorter, and you basically turn up to clinical placements on the wards every weekday. Some of these placements will be in Addenbrooke's Hospital, but you will be sent around the region to other places like Bedford, West Suffolk, Ipswich, Hinchingbrooke, etc.. It's a less intense pace, and many of the exams are more practically focussed OSCEs, with some MCQ and SAQ papers. There aren't essays like in undergrad, though clinical pathology in 5th year formerly was an essay paper. Pathology is often cited as the hardest clinical school exam, but it's not too bad now; it's essentially an SAQ paper that goes step by step through clinical cases, so it's well within the scope of what you will be experiencing day to day on the wards, and with a bit of extra book work it's fine.
All in all, I wouldn't worry about the workload being that much worse than anywhere else for medicine. Yes you have to do essays, but they can be helpful in developing skills in writing that will be useful when writing discussions for publication, and they generally aren't too bad. There's a lot to learn wherever you study medicine, though!