This side Hafren it is a "Welsh landmark", but to the Bristol Evening Post it is an "icon of the West Country". I have linked to the Bristol journal's site because of its account of the history of the crossing backed up by archive photographs. The design was inspired by work in the United States but taken pioneering stages further - there is an outline here.
I was a clerical officer in Ministry of Transport HQ at the time of the opening. I remember what a big event it was, and how staff were encouraged to travel to Aust to be a part of it - but with no financial contribution from the Department, not a great example of man- (and woman-) management.
Talking of finance, I also recall how the tolls were not only expected to pay the construction cost but also build up a fund to pay for maintenance. The South Wales Evening Post is rightly cynical about the way things turned out.