I don't want to say this... but that just wasn't very good. After an excellent third season--the best, most consistent season of science fiction perhaps since Supernatural a few years back--Fringe had a lot prove and the season premiere did not deliver. I'm sure the writers have a long-term plan and it'll get better later on, but for now color me unimpressed. (And yes, I know my expectations for the show were probably too high, which makes me think the episode is worse than it actually is, but that's how I roll.)
If the writers are going to write Peter out for the being, the show should still be as entertaining as it was last season.. However, "Neither Here Nor There" is pretty bland, calling back to the first season when people dealt with freaky things. Lincoln tagging along made things slightly more interesting, but at the end of the day, the case was like many others, except with the added twist that the translucent people are human shape-shifters.
The third season also changed the fundamental DNA of the show, alternating between the blue and red worlds. That worked because there was continuity in the blue world while forging new paths and conflicts fro m the red world. The changes this season are very radical and, from the season premiere alone, not interesting. That's a step back in my book.
The other parts of the episode pertaining to the longer term arc didn't reveal much either and seemed like exposition more than a forward-driving narrative. September is tasked with erasing Peter from time and Peter's image pops up occasionally, with Walter freaking out at the sight of Peter, whom he does not recognize.