This is my first Pride and Prejudice sequel (indeed, I was unaware up until now of the cornucopia of books in this sub-genre!).
Any reviewer would be remiss if he or she failed to remark on Linda Berdoll's diction, so let's address that first: yes, the prose is a deep, deep shade of purple. What many other reviewers seem to have missed is that this is an intentional device that Berdoll employs to mock Jane Austen's style (and indeed, the general diction of the Victorian era). I can understand how a reader can misinterpret this as a serious attempt to emulate Austen; Berdoll walks the line between parody and failed faithful sequel too closely for my tastes. However, in my opinion at least, Mr. Darcy Takes a Wife is an obvious parody of Jane Austen's style, both in it is diction and its characters. I am invoking the principle of charity, because to assume otherwise would mean that this book is a crime against humanity not even I would commit.
Oh, the characters. Oh, the sex. Not only does Berdoll delight in bombarding us with numerous intimate scenes between Elizabeth and Darcy, but she uses Regency slang like it's going out of fashion (which it has). I tended to skim through these scenes, but if that's what you enjoy, then by all means peruse them in as much detail as you would like.
Criticize Berdoll's style if you will, the two main characters are probably more complex than they were in Austen's original novel. We get to experience Elizabeth's burgeoning love for Mr. Darcy and her own trepidation about assuming the role of wife to a man of such high station. In time, we see her take a stand against her husband when she believes he's in the wrong, and fret over his absence overseas during a war, all the while struggling to do what she considers her "wifely duty" and bear Darcy a son. Likewise, Mr. Darcy is torn between his passion for Elizabeth and his lifelong learned attitude of aloofness in society. His new marital status shakes up the status quo at Pemberley somewhat.
I certainly cheered for our two protagonists, especially in their moments of contrived heroics. I cheered when Darcy rescued Elizabeth, and when Elizabeth rebuked Lady Caroline. I blinked in dismay when Major Wickham crossed the line dividing cowardice from villainy. All in all, Berdoll weaves a captivating narrative that, if utterly predictable, is still enjoyable.
The book is perhaps somewhat longer than it should be. Part of this is because Berdoll insists on retelling certain events from the limited third-person perspective of another character. This was interesting at first, and useful a couple of times, but it quickly became redundant. Likewise, certain aspects of the plot might have been condensed--does Bingley really need to father a bastard child? Do Jane and Lydia really have to have so many children? I realize that there's a theme in there somewhere about fidelity, but buried beneath the layers of (what I'm hoping is) irony, it will not soon see the light of day.
In addition to its ponderous length, there were a few glaring errors I found disturbing. For instance, when did Darcy's mother's name become "Elinor"? A quick stop at Wikipedia, of all places, would inform anyone who hasn't read Pride and Prejudice that Mr. Darcy's mother's name was, Anne. This is a classic example of Did Not Do the Research--ironically, according to the Author's Note, this book was originally going to be titled The Bar Sinister, which is the name of a sub-trope of that ilk.
Overall, I suspect that one's attitude toward Mr. Darcy Takes a Wife will be influenced by two factors: whether or not one perceives this as parody rather than straight romance, and whether or not one enjoys Regency romance in general. In both cases, the key to enjoying this book is to not take it seriously (at all). Failure to do so may result in a hernia.