I peer reviewed a paper and found it to be sound - technically and language-wise. How should I write the review report?
Just being well-written and correct is not enough. Why should someone read the paper? What are the new things that we learn thanks to this work? Why is it exciting, interesting or useful? Why should we care about it so much that it should be published in a journal? How is it advancing science? What was the state of the art before this work, and how did this paper change the world?

In your review, you should explicitly recommend either acceptance or rejection. If you recommend acceptance, your review has to convince the editor that the paper is indeed worth accepting. (Similarly, if you recommend rejection, you will need to convince the editor that the paper should not be accepted.)