My first visit to a zoo as a child was to Dudley, then my local zoo, about 20 years ago. I remember being depressed watching the polar bears pacing in their horrible concrete pit, and the gorillas begging (successfully) for food from the visitors in another ugly concrete exhibit. I haven't been back there since, but of course the bear pits have long since gone.
I think any exhibit where the animal clearly shows signs of stress or boredom is a bad exhibit. I have seen such behaviour with the leopards at Cotswold WP, the elephants and polar bear at Prague Zoo and very recently with the ratel and leopard (again) at Edinburgh. In fact, I really hated that row of small sloping enclosures at Edinburgh which house medium/large carnivores (ratel, wolverine, jaguar and leopard). They look at least 20 years out of date. I have even seen one of the elephants at Chester exhibit stereotypical head swaying behaviour. This could well have been the female that was recently introduced to the herd, but even so the paddock there is not exactly huge for a herd of 10.
I agree with one of the earlier posts regarding the gibbon, spider monkey and snow leopard enclosures at Colwyn Bay - all are too small and too cage-like. The gibbons have a long tunnel-like cage which is similar to the Twycross gibbon enclosures (and that's another depressing exhibit, not helped by the proliferation of children's toys which litter the floor). Compare and contrast with the amount of space and height that Chester's and Edinburgh's gibbons get.
I haven't been there for many years but Cricket St. Thomas struck me as a fairly grim place. The leopard enclosure was way too small, and the elephants had a horrible concrete yard on which they were made to perform tricks to entertain visitors. However they do have a very successful breeding record with the leopards, and fortunately the elephants have moved to other collections.