Hardly big leagues, I was left disappointed when I visited. Yes polar bear enclosures are amazing, but then its a field with a fence around it. Signage is disappointing. They could have built a look out for it (covered area) where they could have filled it with information. The big TV screen, bit of a waste.
Marwell on the other hand I enjoyed the visit much more.
For what it's worth, I think both places (currently) have a major, similar, weakness -the lack of anything much to do or anywhere to shelter should the weather be inclement or even just a little showery. I've been around both places in poor (and very poor weather) and it's not much fun. For a non-enthusiast it could be enough to prevent future visits in all but the best weather or could provide such a poor experience they never go back. A large tropical house (regardless of our opinions) goes a considerable way to address this issue and may improve future visitor levels as a result. I hope the Marwell's good and I hope Yorkshire do a big indoor enclosure before too long (whilst I love the place I always think a zoo should make some efforts to show the variety of life -i.e. not so mammal-centric).