Carl Conrad has a review of Campbell’s newest aspect book:
http://anebooks.blogspot.com/2008/11/review-of-campbells-basics-of-verbal.html
He’s generally favorable, though with some reservations Carl is “generally unfavorable, though with some positive comments.”*—both about the book and about aspect study in general. (He is hesitant re. classing the perfect as imperfective as Campbell does and I agree with him in that regard.) As many veteran scholars (cp. Moises Silva in this regard) he’s more hesitant to commit to the details of any particular system. And that probably provides a helpful balance to some of us who have been brazen enough to publish on this subject! 
He says, e.g.,
I really do not believe that the dust has settled on aspect studies sufficiently to say there is much of a scientific or even a more-or-less clear and intelligible doctrine of Greek Verbal Aspect.
He has some other good comments and suggestions for study in this area. Worth reading.
*Carl emailed me that my description was “spun” the opposite direction from what he intended, so I’ve changed the text above to reflect what he tells me that he would have said if he were me writing this post.
