If you haven't read the first three books in the series cast aside the rock and join humanity!
This is by far on of the best books that Butcher (hell, anybody)has ever come up with and I would be including the amazing Dresden Files 'White Night' in that list.
'Captain's Fury' has the same mix of epic fantasy and political intrigue that has made the series so successful while still managing to step up the drama and take the plot and the characters to the next level.
I have to admit that i was surprised that Butcher went the way he did in this novel (i really am trying not to give too much away), but it really strengthens the story and you realise as you continue to read on, that this is what Tavi needs. Also, minor characters are given more of the spotlight than i thought would be strictly necessary but it's never for long enough for us to forget what's going on with our other heroes.
Old enemies like the Vord are not as threatening as they have been in past books, they're more of a dark foreshadowing of things to come. Far from detracting, this allows the already full plot to come to fruition without being rushed. The clash with the Canim is still as brutal as ever, backstabbing politicians are still sneaking around waiting to strike, the First Lord and his cursors are still trying to outrun old age against huge odds and among it all, Tavi's still finding time to stop and see the Leviathans (best scene EVER, hands down).
I've rarely read a book where i've found nothing wrong with it but Jim Butcher is my favourite author for a reason. Even if you're only going to read one Codex of Alera book, 'Captain's Fury' should be the one.