Are zkSNARKS practical?
Proof generation complexity is large but better than previous ideas.
For the verifier the complexity depends linearly on the size of the function the input and the output $O(|f|+|x|+|y|)$ where $y=f(x)$ the computation to be verified for a particular value security of the parameter.
The proof size is constant. 

For more details you can check the papers and implementations in http://www.scipr-lab.org. I think it is the best resource on the subject.