This final part of the Centauri trilogy is perhaps the weakest one - it's a fast read, suspenseful and, of course, leading to the prophesized conclusion... but maybe that's its problem right there: it's too straight-forward, too predictable.
While Durla, the prime-minister, gains ever more power, and starts to resemble Cartagia in his power-lust and self-aggrandizing folly, Londo's getting weaker by the year. Vir's busy leading the resistance-movement (getting veiled hints from Londo), and David Sheridan turns 16 years old. Honoring Londo's request his parents gift him with an old urn, unleashing the ultimate battle for the boy's soul, and, on a larger scale, Centauri Prime.
Much of the culmination was already shown within the series, so that's turning practically the final third of the book into a retelling (In the Beginning, War Without End, just to name a few), albeit with some interesting insights. And of course, the Drakh aren't eliminated yet as a species, they're just driven away at the end - and they might well have lost their hold on Centauri Prime due to their arrogance.
This trilogy definitely was the story of Vir Cotto, coming into himself, much more so than it was Londo's, even if he's the tragic figure who perhaps started all this by allying himself with Morden. But it was also the story of unlikely allies, Centauri, techno-mages, a Narn, a former Hitler Youth-member, in some ways even the President of the Alliance. And it was a story about redemption and finding rays of light where you wouldn't have been looking before (such as Londo and his wife, if just for a short time); but also about overreaching and blinding arrogance and thinking that you can do no evil because you were chosen (such as with Durla, his wife Mariel, and his followers who all turned on him in the end).
But actually, the question of why Londo didn't interfere earlier, was not quite answered. He let himself be bonded to the Keeper because of the Drakh threat to detonate bombs on Centauri Prime... his life and service so that his people may survive. And of course, there was always the threat that they'd turn the next emperor, Vir, into their puppet if he refuses. The decline of his mental faculties was rather drastic, especially in this last novel, but did it have to take another 5 years, after Vir discovers the Drakh with the help of the Technomages, up until he helps Vir reveal the Drakh presence on Centauri Prime to the public? Or did he time it with David's "infection", knowing Sheridan and Delenn would rush after their son and come to Centauri Prime, enabling him to show them what's going on and therefore securing their help? And the other interesting question that wasn't quite solved was whether or not the Drakh plague or Earth could be cured - I realize that they possibly didn't know yet how Crusade would fare in the ratings, which would after all have told that story, and that's why David couldn't explore that facet a bit more, but since Crusade was cancelled, this didn't get resolved (unless it was in the Psi Corps-trilogy which I haven't read yet).
Overall, a good novel which brings all the plotthreads to a neat and plausible conclusion, even if it can't quite keep up the suspense till the end (but again, that's more due to the fact that the end was already known). A definite recommendation for the entire trilogy because one of the main questions, what happened next on Centauri Prime, is finally answered here.