This answer probably differs from person to person, but here is what qualifies as a good critique partner in my mind --
Someone Who Will Help You
I know, simple, right? But really, I think this needs an explanation becasue I don't think it's clear to everyone. A critique partner who does nothing but rip on your work is not helpful, nor is someone who does nothing but tell you how much they like something. To be a truly helpful critique partner in my mind, there needs to be a balance of both.
Let's start with an example --
CP1: This sentence is really weak, and I hate everything else about this chapter.
CP2: There is something off about this sentence but I don't know what. By the way, this is the best book ever!
CP3: I had to read this sentence a few times to fully understand it. Perhaps if you changed the wording to something more like (insert sample sentence) then I would understand it better.
Now you tell me, which partner do you want? I want #3. They are being honest with me without being rude, and they are giving suggestions so that I have an approach on how to fix it.
Which brings me to another point, I want a critique partner who is willing to brain storm with me rather than tell me something is wrong. I know there are things wrong with the book, that is why I am asking for you to help review it. You can't just point out a mistake without giving me suggestions for improvement. Otherwise, I'm stuck.
What else would you add? What makes the best critique partners?
On a completely separate note, feel free to go vote for the beginning of my book in the Project Writeway contest here. Really, go ahead and go. Now.