Your proposal seems to have been carefully though, and I think you are covering all the areas, that's why it's difficult, for me at least, to pinpoint a real question on your ... question.
If the question is if having the form right there, at first sight is going to be good or bad; I don't think there should be any problem and it seems quite enticing. Of course, there are people that just will never leave a review, and some people that will be eager to do it, for those extreme situations, I think that almost no design will change their perspective. But for the people on the middle, that may or may not do participat, having it handy is always a good "help" or invitation, specially since you are removing elements, making it look friendlier.
I wouldn't consider your design as space saver, although it is, I would say it's friendlier. Of course, you can have people thinking that something is missing, who has seen a from without a submit button?. So even when saving space is good and making it friendlier is good, try to let people know that there is something more on that form, may be a simple arrow and a grey band at the bottom part of the form area will suffice.
If the question is about confirming identity, If people don't know that before posting the review, I think you should inform them, at least when the rest of the form appears. You already mention it underneath the email field, but I have the feeling that the idea may not be clear enough, people may think that the review is going to be posted any way and that the confirmation is just for the system, or to make the name/email of the reviewer appear on the page, and that otherwise the review would be attributed to "Anonymous".
About using systems like Open Id, if the target audience may know what that is, you may consider using it, but if the expected target may get confused by it, don't do it. ABout options like Facebook or other sites like that, consider also the audience, are they more concerned about privacy? If so, they won't use a social site login. Also, like with Open Id, can they feel that if the click on a Facebook icon they are going to be redirected to that site, or doing a "like"? If so, don't use it, if the main target audience is familiar with this options or they are flexible enough to understand/adapt, the use them.
Using a honeypot is a good idea, specially if you don't have any other mechanism for blocking them to reduce their impact. Not to mention that it will reduce moderation time. But one question about using them. Is there going to be any mechanism to use the data gathered by the honeypot? Somebody is going to add IPs or user agents to a blocking list? Or the honeypot is just going to work as an instant gate keeper. Because both options are good, but using the data gathered is much more efficient and would improve the system over time.