The two most important things, for me, firstly are honest constructive, neutral, balanced and objective feedback designed to improve the manuscript - and not a means to 'belittle' the author/s. Secondly, that the review feedback is timely. It is frustrating for authors if they have to wait over the 'average' periods of review.
First important thing is Originality of research which is new the form of content and interpretation. Second thing applicability of the content to real situation. These two things are principles for conduct the research and write about the research.