Complex sentence: He felt that the poetry, the characterisation, and the originality of the play were its strengths, but that its major weaknesses were a "puerile" (childishly silly and immature) plot and that it consists of an odd mixture of incidents.
Split into simpler sentences: He felt that the poetry, the characterization, and the originality of the play were its strengths. But that its major weaknesses were a "puerile" (childishly silly and immature) plot and that it consists of an odd mixture of incidents.