When I rec, the most important element is "why I liked this." That's what I look for in other people's recs, too. If a reccer's taste differs from mine, it often comes through in the rec, and then I can work out whether I'm likely to enjoy the recced story or not.

I only rec stories that I can recommend without any major caveat. If I have to qualify my recommendation in any significant way in order to recommend a story... I don't recommend the story.

I should probably add that I'm not interested in being "objective" or "balanced" inmy recs. My enjoyment is a subjective thing, and it's that reaction that I'm trying to convey when I rec.