As far as I am aware, the zoo is closed at the moment for renovation.
I have visited on 2 occasions and It's a nice place to go if you have kids and its not summer, as the kids will love to see the animals etc. But please be aware that some of the cages and places where the animals are kept are not maintained well and it can be quite upsetting. Especially the monkeys and the white tiger they have.
Very cheap to enter I think we paid like 5 riyals each which is equivalent to around £1 each.
Hopefully they will renovate to a higher standard and things will look better once it's finished.
A funny story for you, apparently not long ago, one of the zoos lions escaped and was roaming around Qatar. It seriously would only happen in this country :-D