Entertainment Fuse:
Besides having a title that is a mouthful, Through the Looking Glass and What Walter Found There was distinctly the least gripping episode of the season so far, and it's not for the lack of trying. It featured Walter wandering off unattended, a pocket universe, Peter using his new tech-induced abilities to great effect, continuity from an earlier season filler-episode (or "mythalone" to make it sound more important), and even a not-too-awkward moment of shared grief.
Spoiler:
Peter has turned into the one. =)