In this paper we characterize the Einstein metrics in such broader classes of metrics as almost η-Ricci solitons and η-Ricci solitons on Kenmotsu manifolds, and generalize some results of other authors. First, we prove that a Kenmotsu metric as an η-Ricci soliton is Einstein metric if either it is η-Einstein or the potential vector field V is an infinitesimal contact transformation or V is collinear to the Reeb vector field. Further, we prove that if a Kenmotsu manifold admits a gradient almost η-Ricci soliton with a Reeb vector field leaving the scalar curvature invariant, then it is an Einstein manifold. Finally, we present new examples of η-Ricci solitons and gradient η-Ricci solitons, which illustrate our results.