Panshin is a problematic character in the history of Heinlein fandom and scholarship because although this work was the first book-length Heinlein study, as many have observed here, much of the book is simply a personal attack on Heinlein rather than objective literary criticism. That having been said, the book did contain some insights into Heinlein's work that I found valuable, and I basically ignored the other biased criticisms. I give the work three stars for a pioneering effort and for providing at least some useful insights on Heinlein and his works. But it could have been so much better if Panshin had been able to control his obvious personal dislike of Heinlein.
Panshin and I corresponded briefly some years ago on several topics related to Heinlein's work (mostly on his ideas relating to the Renshawing concepts in Citizen of the Galaxy). I was very critical of his ideas there, but I have to give credit to Panshin who accepted them without ire and the correspondence remained civil throughout.
Around that time, we got into another debate on the Heinlein SIG on the subject of Heinlein's first story, Lifeline, and I thought I would post that here in case people find it interesting, since Panshin has expended a great deal of effort criticizing Heinlein for his supposed faults. So I offer a perspective on that here for Heinlein, and artists in general.
During the discussion, several people commented that Panshin's criticism of Lifeline was nothing more than nitpicking and pettiness. It might be, but I can't disagree with his statement that a later, more mature Heinlein might have written the story better. But it's impossible to disagree with that statement for most artists--it could probably be said of any and all artists--no matter how great.
That having been said, I wanted to make a few more comments about this. I'm no literary critic, and since I am much more knowledgeable about music and art history than literary criticism, I'll use my background there to make my point, since I come at it from a somewhat different perspective.
At least in music and art, it is not the case that even the greatest masters of an art form or genre demonstrate their superiority at every turn. Take Beethoven, for example, arguably the greatest composer who ever lived. He often had technical problems with his musical transitions, those parts of a symphony that tie the other sections together and act as bridge elements.
On the other hand, Schubert and Mendelsohn composed transitions that were smooth as silk, and although they were great composers themselves, I wouldn't put either of them in the same league with Beethoven.
On the other hand, Schubert (arguably the second greatest composer, after his mentor, Beethoven), harmonically wanders around the circle of fifths as if he doesn't understand intermediate harmony at times. However, he is probably the greatest example of the "artesian well" stereotype of a composer. His melodies seem to "well up" from nowhere and he had no problem coming up with thousands of them.
In contrast, Beethoven often struggled with his melodic material. And yet he could create an entire movement in the 5th symphony from a musical phrase that doesn't even qualify as a melody (actually, it's only four notes), being more of small snippet or "idee fixe," as one historian has written. In other words, Beethoven could create a work of genius starting with source material that was quite modest and almost hum-drum, perhaps even minimalist, in a way no other composer could.
This is important, because although there are composers who could more easily come up with melodic material than Beethoven, they still didn't know how to develop it like he could. They might start out with better material, but the "finished product" wasn't as good because they lacked Beethoven's genius at thematic development and exposition.
There are other problems with Beethoven, but I'll leave it at that. If he was a times a little rough around the edges, as in his transitions, he can be forgiven for this relatively minor problem because his contributions in the most important areas were so amazing. To mention just two of these, he greatly increased the complexity and sophistication of harmonic and symphonic structure more than any other composer before or since.
Another way of thinking about it is that Beethoven, like Heinlein, was a pioneer and trail-blazer who revolutionized our thinking about music (or science fiction). If they're both a little rough around the edges at times, I don't mind that--as the refinement of a field can be left to the lesser artists and those who follow after (which is essentially what happened). And the same goes for the subsequent development of science fiction.
I'm sure this idea applies to great literary figures as well, and so I suspect the same thing could be said about Heinlein as about Beethoven. As I said, like Beethoven, Heinlein wasn't just another competent artist who just "upped the ante" a bit; he was a revolutionary who blazed new trails in SF writing, going where no man had gone before.
No artist or writer is perfect. Even if Heinlein had a few minor faults, as Panshin has maintained in this book, they pale into insignificance in contrast to the greatness of his overall contributions, just as Beethoven's do.