For me - worth every moment. I did medicine.
From an academic perspective - I loved the tutorial system - it was very stimulating and there was nowhere to hide. Excellent preparation to be able to organise an argument, defend it and be able to reexamine your hypothesis on your feet in an cogent fashion when new ideas or data is thrown at you. I am an extrovert, so like to do my thinking in external space, so this suited me very well.
For medicine specifically, the undergraduate grounding in basic medical sciences (whilst not trendy) does, I think, stand you in good stead, as you are able to work more out from first principles rather than have to remember lots more facts.
The other nice thing is that it is possible (albeit unusual) to do something less obviously related in your third year BA, compared to the intercalated BSc offered elsewhere.
I would however say that the teaching during the clinical part of the job was much less structured than what I've been involved with subsequently at some London teaching hospitals. It was a lot more self-directed and sink or swim. But this may have been good preparation for the job and certainly the postgraduate exams. It may of course also have moved on through the years as well.
From an experience/extracurricular perspective, it was great. My college had 100 in a year, and was one of the relatively larger colleges. This meant that you did know most people. It gave me a lot more mixing with people reading other degrees than I think I would have had at medical school otherwise. Also, there was a lot of opportunity to get involved in new activities and sports. You could play for your college beer team even if you were a novice/a bit rubbish. You didn't need to be Blues level to get a look in.
Does it give an advantage in the job market afterwards? It shouldn't really for Medicine. It has a fairly rigid career progression. I have been involved in interviews for most levels of doctor. There are no extra points for Oxford or Cambridge when shortlisting. I can honestly say that I don't think about it when interviewing. However, making sweeping generalisations, they do tend to get through the professional exams in the fewest attempts, and do tend to be successful later on. However, this could be a number of different factors including shared personality traits like being even more hypercompetitive and needing the validation of being at the top than the normal doctor!
I count myself as extremely privileged to be able to have had that experience, and I would encourage young people not to discount it as being too clever/too posh/too weird for them. Some colleges have a ruthlessly academic reputation and some do have a high proportion of ex public school boys. However, most of the others are quite normal.