Energy barrier effect on the transient nucleation kinetics is studied. For a high barrier case an advanced interpolation of the "boundary-layer" type is suggested that is valid for the entire time interval. The nucleation kinetics for the "nucleated cluster" size n(c) is described, the lag time estimate for n = n(c) is given. For a low barrier case a new "similarity" solution is reported. It is shown that analytical results provide an adequate description of the transient nucleation kinetics (in comparison with numerical solution of governing equation) for both high-barrier and low-barrier conditions.