Like the Pax airlines, the freight airlines run from good to unbelievably bad. The good ones like FEDEX and UPS are well run, pay good, and have union contracts. The bad ones, like the scumbag 747 outfits in the states pay poorly, no retirement, 20 workdays per month often extended, lots of DH that you're barely paid for, marginal equipement, and treated like scum by management.
So can flying freight be good? Yes. Can it be really really bad? Yes.