Both critical and systematic reviews have the same objective (i.e., to synthesize studies on a given topic). However, a critical review does not do so in a standardized way as a systematic review. Protocols and quality assessment are defined a priori for a systematic review approach.
For more information see the following references:
1. Kitchenham, B. (2004). Procedures for Performing Systematic Reviews (p. 28). Technical Report TR/SE-0401 and National ICT Australia Ltd.
2. Biolchini, J., Mian, P.G., Natali, A.C.C., & Travassos, G.H. (2005). Systematic Review in Software Engineering. In Technical Report: Vol. ES 679/05.
"The systematic review intends to find out the appropriate answers to the questions that have been developed in accordance with the research problem in a study.
The function of the critical review is to make a critical assessment of a research idea proposed in a study by comparing various scholarly studies that have been already undertaken on the subject"