For context, whilst I apparently registered on the site in 2011 I've only really paid any attention to it for the last 3 or so months and I've been answering for less time than that which probably puts me still firmly in the newbie camp.

I'm not a huge fan of the canned response suggestion (from either side of the process).

From the reader's perspective:

• If I start reading exactly the same sentence that I've read before it's going to make me tune out. There's a good chance that I won't get to the good bit at the end of it. For the particular OP that posts the code, a lot of the information might be new. However, for the regulars I think it will very quickly start feeling samey and boring.
• I think it's also going to make reviews feel a bit disjointed, with this canned response bit sounding like '@Phrancis', the next bit sounding like '@N3buchadnezzar' and then a bit sounding like the actual person attributed to the answer.
• I know one of your goals is to try to provide more space/time for the reviewers to be able to concentrate on the interesting bits of questions that aren't covered by the paragraph starters, however I'm concerned that it might lead to users simply rolling out reviews that consisted simply of any of the suggested paragraphs that were vaguely relevant and then didn't really go further into the code, essentially lowering the level of contribution, rather than increasing it.

From the writer's perspective:

• I don't find lists like that particularly approachable (i'd rather type the same paragraph I've typed a hundred times in a slightly different way than go and find a canned response for that particular item). In most cases, between window switching, searching and copying it's going to be faster for me to just type it anyway. For it to work for me, I'd need to create a template that had all of the things I might want to include in the review, copy and paste the whole thing and delete/expand as appropriate. This would make the reviews look more and more alike.
• I have my own style. I wouldn't say it's an overly polished style, however it is mine and I don't especially want to sacrifice it by using somebody else's snippets at the start (which is arguably the most important point) of any review.

So what's the alternative?

I don't have a stand out alternative. I have thought about creating a checklist of things that I would want to check in a review. I think this might be useful, in the sense of not forgetting things however If I'm honest, I probably wouldn't use it. When I'm reviewing code, I like to be led by the code I'm reviewing, that's part of what makes it interesting. If all it's variables are 'x,y,z' then it screams naming issues. If it's using lots of globals, then they become the dominant issue and I might not be as bothered by a few bad variable names. I think this is part of what's compelling about the site each review comes from the perspective of the writer which is based on their experience and approach to code. If we start relying on lists I really think we'll lose that.

The documentation beta on stack overflow is interesting in a sense. I can see how it could actually be very useful in the context of providing review feedback. Having examples that you could link to as part of reviews in a known place as part of 'further reading' could be useful. One of my few contributions to the sql documentation is a common mistake that impacts performance. Having a strategy for collecting something similar for 'examples of improvable code style', (for example 'names matter' comparing a well named section of code with a single letter named section of code) might be useful. It would be nice if this could be hosted on CR, however I don't see that happening any time soon.