Is the mean-field approximation so bad? A simple generalization yelding   realistic critical indices for 3D Ising-class systems
  Modification of the renormalization-group approach, invoking Stratonovich transformation at each step, is proposed to describe phase transitions in 3D Ising-class systems. The proposed method is closely related to the mean-field approximation. The low-order scheme works well for a wide thermal range, is consistent with a scaling hypothesis and predicts very reasonable values of critical indices. 
A.N. Rubtsov