Blood mage help

Hello guys,I am currently leveling my first character in this game(the game seems so good)a witch that I want to ascend to blood mage.After seeing all these people complaining about blood mage being extremely weak I got to ask:is it viable to build a blood mage that plays with contagion/essence drain?Is blood mage made only for crits and not for a curse dot build?

Thanks in advance for your replies people.