Are descriptive comments in the review required?

Yes, the descriptive comments are required. If your decision  is to reject the manuscript, then you have to explain to authors why  you are recommending the rejection. If you are recommending major or minor revision you have to write to authors how they can improve manuscript. If your decision is to accept manuscript you should justify your decision in confidential comments to Editor why manuscript is accepted. Please notice that new and technically correct results are not a good enough reason for manuscript acceptance. Before accepting manuscript you have to list issues from the manuscript which give a manuscript a chance for citations. This information need not be sent to authors but it has to be included in box of confidential comments to editor.