Saga is no Hellboy. It's worth reading for some of the surprising moments and characterization, but it's not a classic.
It was hard for me to look at other illustrators' besides Mignola working on Hellboy, and kept me from even cracking open any issues of BPRD. But when Mignola farms out the visuals he does it as a cartoonist; he directs appropriately. The results are competent.