On re-reading, I have to agree. Re-reading Harbinger, despite knowing everything that happened, was still incredibly gripping. This just wasn't. Ward and Dilmore obviously made a strong effort at continuing all of the amazing things Mack set up in Harbinger, with sweeping plot developments and character arcs with a bit more meat to them than usual Trek fare, but weren't quite up to the task. The plot development is slow and the characters are just a little bit less sparklingly awesome.
I do think Ward does better in Open Secrets, and I haven't read What Judgments Come yet, so I can't comment on that. I'm fairly certain this will end up being the weakest Vanguard entry, though. Lots of good ideas and solid developments, but it just isn't written especially well. (Granted, I'm comparing to Mack, who's one of my absolute favorites, but still.)