So the second best review of Polaris is by John Snead. I call it "a review" but it was really just a livejournal comment. It is this.
"The entire concept of Polaris utterly repels me."
Why is this so good? Let me try to hit a few points:
1) It is concise. Not saying that all critiques and reviews must be short (def. not this short), but it says exactly what it wants to say without mincing words. I've seen much much longer reviews (1000s of words) that contain much less information.
2) Like all good critique, it is a personal expression. John is expressing his reaction to Polaris. He's not trying to make a universalizing statement. He doesn't have to. He's trying to express his own experience of the work, which he does well.
3) It is well written. "utterly repels" is a great turn of phrase. "The entire concept" shows that it is not that he thinks that game is poorly executed, but that he finds the basic concepts of it repellant.
4) It is truthful. At the time that he wrote this, I didn't know John at all. Now, through odd coincidence, he's a friend of mine. Polaris is absolutely a game he will not enjoy if he plays. He is right to be repelled.
5) It communicates with the reader. To both me and the person he was responding to, it said "this game is absolutely not for me." To the general audience: if they know the sort of things John likes, they will know that Polaris is not those things. To me: If John was in my target audience for the game, this would indicate to me that I was seriously screwing up my presentation. As it happens, he's decidedly not the target audience, so it's indicating to me that my marketing is working well: I don't want to attract people who won't like the game.
So that's the start of providing a good critique*: Be concise, express yourself, write in good style, tell the truth, communicate clearly.
* I'm not strongly differentiating between review, critique, and design-process feedback here. Not because I don't think that there are important differences, but because what I am saying here applies to all of them.
P.S. John, if you read this, I hope you're okay with me using you as an example here.