The brilliance that was the first part of the Mirror Duology concludes (just in case the title of the episode doesn't explain that already).
In what is essentially a celebration of everything that made the series what it was while having as much fun with franchise lore as possible, Archer and several other members of his Mirror Universe crew don Kirk-era uniforms and battle the rebels who are trying to thwart his plans of seizing control of the Terran Empire, including T'Pol, Soval, and Phlox (this scenario is also ironic, given the events of the Terra Prime Duology that follows).
We see a CGI Gorn this episode (following a CGI Tholian in the previous entry), but the real thrill is watching Archer truly enjoy himself, and how the episode quickly centers itself around Hoshi (making this her lone spotlight of the season, though very welcome) in its conclusion.
It's all ridiculously clever. One of the more inspired elements is the alternate opening credits for both episodes, which feature an evil version of the clips that are normally featured, and a new theme!
Not without exaggeration, but if the Mirror Duology had occurred earlier in the season, or series, fans might have finally acknowledged the effort put into Enterprise and rewarded it by, y'know, watching.
franchise * series * essential * character
Memory Alpha summary.