I prefered Deathfire in the trilogy. Old Earth had to juggle three plotlines, one of which was supposed to be its own novel before crunch, and it shows.
The perpetual storyline feels tacked on like an afterthought, basically an extended clean-up job to wrap up loose ends from Dan's Cabal books, without really saying much on its own. The Iron Hands plotline felt like the meat of the novel, but was concluded two thirds in, with Vulkan being relegated to the role of bystander for most of it, and the third of the book he and his dudes get felt reasonably shallow and forgettable. I seriously do not think that the last chapters dealing with Vulkan's arrival on Terra had any of the oomph needed for a real climax, so it felt pretty flat after that of the Meduson arc. It was more of a sightseeing tour from Mount Deathfire over the latest Heresy battles through the Webway onto Terra and into the Palace, and considering that Deathfire was the journey/odyssey novel, this one felt less interesting - especially since Vulkan doesn't communicate as much as he should, and so when things happen, they happen with little preamble or anticipation.
Is it worth reading? Yep. But I wouldn't consider it Kyme's best novel by a long shot. None of the three main plotlines got as much time to develop as they really needed, and while that is least obvious (though no less regrettable) with Meduson, it limited all three. I wonder what Meduson's finale could have been, or Vulkan's journey to Terra (and maybe an actual job to do there before the end?) if it hadn't been for the fact that the novel had to accomodate so many different things with relatively little overlap.