I see it like this: there is the review section to give supportive and maybe light reviews. There you can point out a what ever comes to your mind directly after reading. There you can let the author now in general what you thought about the story and how you felt after reading it. Sending personal messages to the authors is something I'd also do, especially if you want to give/get specific criticism. It is always nice to ask if they want it though. I love interacting with other authors.
In public reviews I seldomly leave negative comment's but I think I can see some good points every single story I have read. I have no need to put myself above others and try to find the holes in the stories. If I don't like them, I just generally move on fast and read something else. If the author has put their heart and soul in to the story, I appreciate it.
I never read stories written by people I dislike. That is my choice. I would never leave a neg comment because of my personal feelings about the author, so I just rather skip the story.
I feel it is ridiculous to put oneself above others and comment from high up there that some story doesn't deserve a) the amount of reviews b) the positive reviews c) the rep points d) the hype... I'd say everyone feel free to WRITE, READ and COMMENT, instead of scrutinizing other peoples actions. I think being polite has nothing to do with sucking up with people. Being nice has nothing to do with lying. Being active and supportive to your friends is not away from others. There is a line between constructive criticism and negative criticism.
Respect and be respected. I would not want to see GA turning into this competitive dog eat dog world.
With this said, I still personally would love the honest feedback. It just shows that the reader has actually read the story, focussed on it and wants to offer the author advice. I'm thankful of the feedback I get, I try to get learn from it even if I don't always agree with it. Via PM I have gotten a few pretty honest feedback that did not praise my work, but were left with thoughtful insight, humour and support. I treasure them most.
The biggest truth came from Collan: all authors take feedback differently. Some never see any flaws in their own work. The fact just is that not everyone can be pleased - not the authors or the readers.