I dislike Noah's Ark Zoo Farm (as many on the site do) for ideological reasons, but if one can push that aside, it's a decent zoo. A lot of wasted space, but with Europe's largest African Elephant enclosure and a solid collection of venomous snakes, it certainly isn't bad. Similar things can be said about the Aspinall collections. I am strongly against Damian Aspinall, but I have to admit that his zoos are quite good, as long as you like primates and are willing to put functionality before aesthetics!
But you are right,
@TortoisesAreTerrific , the only truly bad zoos are the ones where the animals seem miserable or poorly-treated. I don't think any zoo that I have been to matches that description. There are bad enclosures, but that doesn't translate to a bad zoo. For example, I really dislike the Red River Hog enclosure at Chester, which is small, unimaginative and does absolutely nothing to represent the forest habitats in which these creatures naturally dwell. But I would ever call Chester a bad zoo. In fact, I would probably state that it is the best zoo in the country.
If you want my least favourite zoo, then it is Noah's Ark or the Aspinall collections. If you want the worst zoo in the country, then it is certainly *not* Noah's Ark or the Aspinall collections. I don't think that any UK zoo matches that description perfectly, but I would love to hear what zoo-goers who are better-travelled and informed than myself think on the matter.