In general, it seemed pretty professional.
There was one pretty small thing that I (as a parent) picked up on - There was some concern about the fairness of the architecture assessment/essay across different colleges - in some, the porters gave a tip-off as to what the drawing was going to be of, and in another case the invigilator looked up (on Google) a key term that was part of the essay. In my view, it's unlikely that either of these things actually affected results, but it did result in "raised eyebrows".
There was perhaps an inconsistency in "friendliness" of interviewers across different colleges. Again, not at all convinced that this was significant.