When I switch from Intel HD graphics 4000 to GTX970, it began to have those white blocks :< Devs do need to pay some attention to that. EDIT: game does seem to run well under low graphics (HD graphics 4000)though
Just choose Righteous before you get all the boons. Fire of Gods is simply OP. I use 3 x Divine Glow (Divine Mode) + Dauntling Light (Empowered), which works pretty good for me.