So, one of the things I do as a part of my life as a writer is read and critique manuscripts for friends, students, proteges, and other fellow writers. This can be entertaining, educational, frustrating, and rewarding, all at once or by turns. Over 15 years of doing this, I've developed a number of personal rules on the topic. The main ones are thus:
1. Always tell the truth.
2. Always be constructive.
3. Always try to help the writer achieve their goals. Or, Don't try to make them write the story I would have written from the same premises.
4. Sometimes following rules 1-3 means recusing yourself.
2 is easy, 1 and 3 not so much, though 4 can help with that. Everyone has personal reading biases and tastes, things that work for them or don't for reasons completely unrelated to the comparative success of the work. For example, most time travel stories don't work for me. That includes any number of award-winning works that are loved by lots of other readers.
So, if someone gives me a time travel story and it's not working for me, I don't go into great scathing detail about the inherent problems of paradox and meaning. None of that is going to help the writer and it's likely to aggravate both of us. Instead, I recuse myself and politely let them know that I'm not a good reader for this particular story. This can also be frustrating for both reader and writer, but hard experience has taught me this is much the better choice.
Any thoughts on recusal? Types of stories or themes that don't work for you? Rules for critiques? Stories of critique where you should have recused yourself, but didn't?