I am still baffled, a week later, by this episode.
Smallville is finishing a TEN YEAR run. They have built up such a rich heritage for the show. They have just 135 minutes of episode time left after this episode to finish the legacy. And they create THIS. Why?
It's just... baffling. It doesn't further the story. It doesn't fit with the arcs really. It doesn't close off any stories, or revisit any memorable moments. The style doesn't fit, it feels like a director having a laugh and emulating Spartacus. It's not interesting. The return of Zod just slows down the pace of the last season.
All in all, Smallville season 10 has been (overall) one of the best. But this episode just smacks of filler until they get to the finale. It really adds nothing to finish this great show.