I don't really have a lot to say about this book, because I don't really care much at all about Enterprise or the Romulan War. And, unfortunately, this book didn't change my opinion on either one.
I expect people who like Enterprise will have a much more positive response to the book. It's big and sweeping, with a large cast of characters, and a chain of events spread out over several months. It continues all the storylines from its predecessor, dealing with the fallout of the Kobayashi Maru situation and the beginning of the war with the Romulans.
The thing is, the book feels like it was assembled from a number of pieces that had to be fit together carefully -- ongoing elements from the Enterprise novels as well as bits and pieces of information about this era from episodes of Enterprise and the original Star Trek -- and as a result, it feels paradoxically like there's a lot going on but not much really happening. (It's the same way I felt after reading Forged in Fire and The Red King -- damn, that was a long book, but nothing much happened.) It's also so plot-driven that the characters suffer. The Voyager novel Full Circle had a similar job to do, fitting a lot of puzzle pieces together, but it did so with some powerful character-based storytelling. There was something to hang onto beyond watching the movement of the cogs and gears.
Beneath the Raptor's Wing also feels a bit unbalanced. Some new characters who have a lot to do early on suddenly disappear for hundreds of pages, only to make brief appearances later on; other new characters appear only for a page or two, to add their mosaic tiles to the big picture. Characters make odd choices without much in the way of rationale to make everything fit the few contradictory bits of information we have from canon. I blame the writers of Enterprise, the TV series, for this; the way they used the Romulans on the show makes it hard for anyone to expand on the story and still stay consistent with the few essential bits of backstory from "Balance of Terror."
I still don't buy Trip as an undercover agent at all. I don't buy his decision to stay on Vulcan near the end of the book. I don't like the way the plot seems to require certain characters to be stupid at key points, or to fail to ask obvious questions.
I'll read the next book (hoping all the while that this is no more than a duology), should it be published. I'm not looking forward to it, though.