He may be the only thing worth watching on it, but aren't the young FBI agents (The Mulder/Scully clones) the supposed leads?
The sense I get is the writers view Olivia, Peter and Walter as the primary characters and who the focus of the stories are directed while Astrid, Nina and Broyles are the supporting cast.
Astrid is not much more than a glorified but amiable extra. Nina is hardly seen anymore but I always found her intriguing. Broyles is okay but nothing to exciting. I actually preferred him on LOST as Abaddon who himself was not much more than a plot device. Strangely enough season one's enigmatic Mr Jones was a far more interesting character than all of the others in my opinion. Olivia/Peter lack the chemistry--platonic or otherwise--that Scully and Mulder had and what made TXF such a wonderful viewing experience.
Personally I really like the show, it started out a bit of an X-Files clone but it goes off in it's own direction late in the season. But they have X-Files style eps. even into the second season.
The problem isn't that they do freaks of the week type stories--the problem is that they aren't the least bit fresh or clever with any sort of interesting spin or twist. It pretty much is straightforward as we sit through the motions as they go from point A to point B by the end of the hour. It also has a bad habit of being formulaic in that some mumbo jumbo gadget saves the day. Those were big problems in season one and the only time we got a break from that was with the mythology episodes which injected some genuine mystery and suspense as to what is going on and what would happen next. That is why the show desperately needs to be the kind of heavily serialized show that LOST or season one Heroes is/was. It forces the writers to carve out a unique identity for the show.