Wroclaw is one of the very best zoos in Europe; its collection and its design are both superb (even if there are, still, one or two dusty corners).
I think Opole would possibly merit being described as very good! it has been almost wholly rebuilt in recent years, and as a consequence is a strong, modern, European zoo, maybe a little unexciting species-wise, but certainly a place worth seeing.
Personally, I like Warsaw very much indeed, both as a zoo and as a city. It has major flaws, but much to commend it.
A number of the zoos in Poland's other major cities - Plock, Lodz, Kraków, Katowice - have good elements, but, overall, are in need of improvement. In some cases this improvement is underway, in other cases it is promised, and in some cases it is unlikely.