I review from two perspectives, editorially and critically. From an editorial perspective I try and assist the author in matters of grammar and composition. Good editors help authors get better. From a critical perspective I try and analyse what I liked and what I loved. Critical reviewing should allow the author to bask in the glow of achievement and to alert other readers.
Unlike in the real world, when something sucks I don't have to go into detail why it sucks. Believe me you have to use a lot more keystrokes to shoot something down than to praise it. Therefore here in fantasy land, if I don't like it, I don't have to review it!! YEAH!
Lastly, I like authored reviews. If somebody reviews my writing, I like to go and read their fiction, see how they did it. In my sixth decade of life I still feel that I am learning. I don't care how harshly you treat my prose or trash my fantasies but I want to read what you have written. In the world of Science and Nature not knowing who has shot your paper down really sucks (although you can often figure out from their sytle and what they said who they are). Since we are here at the cutting edge of the avant garde and most of us are using psuedonyms, let's be straightforward.