For me, I really wanted to like the books because the concept sounded so awesome, but after reading the first four books (well, like mini-books really, I think it was a serial novel or something) it just seemed like standard PAD.
Super referential to the point of distraction (constant references to the various shows as though PAD is winking at us on every other page saying "Yep, it's Star Trek!", with practically every character somehow connected to TOS or something, one guy even descended from Apollo in Who Mourns for Adonais), lots of hokey joke characters mixed in with really 90s like "X-treme" stuff (see Calhoun's backstory and character, complete with facial scar and purple eyes), and his description of Shelby didn't much resemble what I saw on television other than the blonde hair.
I know he has a lot of fans, but I personally couldn't enjoy the work. I wonder if the books didn't so much jump the shark as the people reading them have gotten older and developed higher expecations. With the quality of Trek books having gotten so much better what once seemed top of the line became kind of average. I was able to push through the first four books because the overall plot was interesting even if I disliked the execution, but now having read things like Vanguard I don't know if I would be able to make it through something like that again.