The final installment in any series always runs the risk of being a massive disappointment. Thankfully, Invincible does not suffer from this malady. This will be a short review through necessity, because any great description of the plot will ruin it for everyone not yet caught up.
Needless to say, Troy Denning has really rolled up his sleeves and got stuck into the gritty nature of civil war (expanded to galactic scope, here) and the tragedies and attrocities that war can compel people to commit.
Invincible is more brutal than pretty much any previous Star Wars novel or movie. The battles between Jaina and Jacen/Caedus are described in amazing, gruesome detail - so much so that you almost feel like you're actually there.
Perhaps the reason Invincible doesn't fall foul of last-installment pitfalls is because it's not, ultimately, a last installment. There will be more novels to come with the characters we all continue to love (next up, chronologically, is Millennium Falcon, out at the end of this year).
Excellent plotting, excellent humour (though not too much), and allegory done very well and deftly, Invincible is one of the best Star Wars novels to come out over the past few years (it certainly blows all of the previous long series out of the water). If you haven't started the Legacy of the Force series yet, get cracking so you can get up to speed and enjoy this cracking final chapter.