Birds really is Warsaw's strongest point. Primates are decent as described in the last round but I think birds is where the zoo excells. Check the gallery for some pictures of the birds and bird enclosures and if I have time I might be able to write some more (though I'm not sure I will).
It's worth pointing out that Warsaw's collection of bird rarities is unusual among zoos in that it's increasing. The zoo seems to acquire more bird rarities every year especially within the director's specialisms of pheasants and doves. (I'm aware that not all will view this as a positive)
The housing also seems to be getting better with new larger aviaries regularly being built in addition to the really nice bird house. The zoo also does quite well breeding many of their rarities.
What's Wuppertal like for primates?