Although I often wish British zoos would be a bit more creative, not every zoo can offer an immersive experience along the lines of Snowleopard's assumptions on what makes a good enclosure. I enjoy his posts but his views are far from authoritative in my view.
I have quite an American view of great exhibits in that I think an exhibit is truly enchanced by well-done theming and immersion. There are so many benefits to this, in that it looks nicer to the public, it is generally far more educational than a sign that will get overlooked [people pay more attention to the small cinemas/speakers, and the 'story' of the exhibit. But of course, all of this adds to the cost of an exhibit.
If a zoo can afford immersion exhibits then that is what's best, but if a zoo can't afford a £4 million tiger exhibit then where is the problem in them building a cheap 'Marwell/Howletts' style exhibit to house them? Doesn't look as nice, but it's practical and cheap.