I don't know about everyone else, but this season hasn't been doing it for me. Hopefully this changes with Peter's return, though the first four episodes give me little confidence.
My biggest problem has been the lack of momentum in this opening arc. There's no urgency. Now that Peter isn't in this world, what has changed that makes it so necessary for Peter to return? Nothing. Olivia is doing fine, Walter is a bit kookier but Olivia is there for him, and the two worlds aren't at war anymore. Peter could be taken out of the show completely and it'd be a lot like the first season.
I think point this out every week already, but the third season had a much better start with the immediate predicament of Olivia trapped in Earth-2. That was a human struggle where both sides were understandable. In this season, though, there just a big mystery hanging over the season regarding Peter's disappearance. And really, we have no idea what's going on because only the writers know how the sci-fi mechanics work on the show.
"Subject 9" is a pretty slow episode and not much happens, but like the rest of the episodes this season, it has stellar scenes of Olivia and Walter. We get a look back at the Cortexiphan kids and the harm Walter caused in the past. The episode ends with an expected twist, the return of Peter, which should bring some much-needed excitement to the next episode.