I got 3As and a C at A-level back in 1991. It wasn't quite good enough for Cambridge (I had no interview preparation) but I had my pick of what's now called "Russell Group."
I'm now a teacher (a career changer so there was a long gap between my A-levels and degree, and entering teaching).
As well as the obvious changes - the vastly increased numbers of students doing A-level and the marketisation of the University system - I'd say the main change is access to information.
My students have past papers, markschemes, examiners' reports (those are gold dust!), excellent revision guides, excellent free revision videos and accurate, up to date current affairs information (important in my subject) is available at the touch of a button.
We had Letts Revision guides (which I don't think were even available for A-level) and whatever notes we'd made in class. You were often completely dependent on the teacher being decent. We were never told what was on the syllabuses!
Things are much more democratic now in terms of information. You can get round a poor teacher (I taught myself stats but that was possible because there was a decent textbook - those were really lacking in e.g. History then).
There is a lot of outreach from universities especially to poorer and more diverse students.
Parents are much more involved in education in many cases.
Sadly there are also a lot of students taking A-level who really would be better suited to a vocational course or the workplace.
It's a totally different world.