I have to agree with you, that the polar bear enclosure is a huge downstep in comparison to the rest of the Eismeer, but i feel like the enclosure is bigger than it may seem. The main flaws of the exhibit are in my opinion the lack of natural substrate, not enough amount of land and that the enclosure is mainly surrounded by huge walls. On the other hand the enclosure has some aspects i really like, it has a lot of altitude difference allowing the bears to climb up to a height of 6m, the pool is sizewise good with depth of up to 4m (i think), adding to that the exhibit is great for the visitors and the view onto the enclosure right behind the walrus exhibit is just outstanding. Overall the enclosure is definetly not a really good enclosure and dissappointing in comparison to the rest of the Eismeer, but it`s not unbearable and doesn`t ruin the whole Eismeer as a complex.