As a reader I prefer a more positive review because otherwise I'll often get talked OUT of reading the story. For example, I was going down a list of recs from someone who gives all the caveats and she is like "Amazing story, well, needs a beta really a lot but..." and I'm thinking, do I really want to read that story? No. The truth is, I probably wouldn't have noticed the typos myself or wouldn't care, but now that it's been said I would be looking for them and that ruins the story for me. Also something like "Amazing story, just ignore them screaming as they come" also gets in the way. It's already difficult enough to suspend disbelief for certain romantic scenes, but when you know someone else disbeliefs along with you it's near impossible.

So as a reader I would rather not know until I had a chance to make up my mind. This is of course only for people whose recs I trust. But establishing or ruining trust is easy. If after 5-10 fics I see that our tastes match/don't match I go from there. I don't assume that the reccer owes me to provide a good story, I assume they reced it because they liked it.