This is a good, fun episode that introduces the notion of a parallel universe.
One major thing that has niggled me even since first seeing this episode is it being stated if one person dies in one universe, they will also die in the parallel universe. If this is the case, why aren't people suddenly dropping dead all the time?! The rather 'Star Trek'-y way that I've personally explained this away is that it only happens on the rare occasions when the two universes are directly in line to each other.
Once you get beyond that nitpick, this is an enjoyable episode that doesn't take itself too seriously.
I really like the imprisoned Iolaus' line "I am not a numeral, I'm a free man", a nice homage to the cult 1960s series 'The Prisoner', of which I am a fan.
It is fun to see everyone acting as their own opposites; I've always loved evil twin stories. Kevin Sorbo even has the compulsory goatee beard as the Sovereign.
Like my fellow reviewer, I am a big Gabrielle fan and was a little disappointed that she only had a one-line cameo in this story.
This parallel universe is actually quite unusual in that in all other time-lines and universes and whatnots, Xena and Gabrielle are always instinctively drawn together.
I also really like the moment when parallel Xena uses her shoe as a would-be chakram, and the line "I guess I must have more skills than i thought", a nice play on regular Xena's oft-used line "I have many skills".
The only person missing from the parallel world is Salmoneus – I would have loved to have seen a parallel version of him, presumably kind and generous with his money.
The story itself isn't bad. I find once the novelty of the parallel universe has started to wear of, it does start to sag very slightly in the middle, but picks up again for the end.
You can tell they had a lot of fun making this one, and that comes across on-screen.
All-in-all, if you're willing to look past a few nitpicks, this is a fun episode.