I've just finished reading Ravenor Returned, having already read the Eisenhorn trilogy and Ravenor.
While the 1st person perspective for Eisenhorn and Ravenor is a bit strange at times and took a bit of getting used to at first, it Dan Abnett definitely works it well. Also, before people get worried about it being badly written, it's only used for those sections where the Inquisitor is involved in the action, so it makes sense.
The imagery of the various Administratum buildings is great, and I can see how it fits with a combination of technology and machine worship.
The end was certainly interesting, and I'm not wondering if there's a chance of a follow-up to make a trilogy, like Eisenhorn had.
I've got an idea as to how Slyte fitted in to everything, and what happened to Zael, but I think Abnett pointed towards it rather than clarifying all of it (unless I just read it and missed a bit).