I found walking around Cardiff very enjoyable. A clean city not overcrowded with tourists. Of course it could be because we visited in January and it's really cold and rainy outside but I got a very nice impression about it. I have been to plenty large UK cities and some of them were less then great and sometimes even scary.
Cardiff however I liked. I love the fact that they have a large walking area in the center with plenty of shops and pubs offering food for little money. In general I found Wales to be a very clean and inexpensive country. I would love to visit again someday.