I half-liked it. Quark is great, but Rom is Jar Jar Binks.
I love the idea of the episode. A Ferengi story! How great is that? It's pushing Quark into actions that could almost be deemed heroic, yet at the same time he's still a greedy, selfish scumbag who'd happily sell an ultimate weapon to the villains. We see him do just that. It's funny. There's so much subversion you could do with him. I just about killed myself laughing at his prayers to the Blessed Exchequer, for instance, although a bit of googling shows that that's not original to this episode.
Quark loves Ezri. He does his duty to the Grand Nagus Zek. He even gets to be cool.
"Are you suggesting we go back home?"
"It's the smart move."
"Do we look smart to you?"
He's also played by Armin Shimerman, for whom I have a great deal of time.
His brother Rom, though, really is Star Trek's Jar Jar. He's better acted (i.e. not a children's TV presenter), but his stupidity breaks the show. The episode is garbage because it's got Rom in it, even though otherwise I liked it. He just goes on and on, dribbling forth dialogue that I'm going to hypothesise is meant to be funny. I didn't even believe that I was looking at a person. He's unconvincing on the most basic level of being a credible as a character in the fiction. He's just an annoying comedy routine, although in fairness I was amused by the twist of Rom being the one who can fix the cloaking device, outwit the villains and save the day.
There's also another Ferengi, the Grand Nagus Zek. He looks like Warwick Davis's Leprechaun in that low-budget horror franchise and his personality's a bit annoying, although less than Rom's.
I repeat: I love Quark. It's the other Ferengi who drag the episode down, as if the show thinks greedy amoral backstabbers need to be played as comedy idiots.
As for the mirror universe, it's dull. All significance and edge has drained away over the course of its Deep Space Nine appearances, leaving us with cameo roles for the regulars that might as well have been comedy routines. Mirror-Kira is wasted. Mirror-Worf gets a funny bit (punching a subordinate), but he's still inherently uninteresting, because he's Worf. He always chooses the most one-dimensional option and he's seems actively hostile to being intelligent. Let's execute the Ferengi! No, wait, we need them to fix the cloaking device! Let's execute the Ferengi! Why? Um, let's execute the Ferengi!
How can the mirror universe have become bland? That's like a crime against television. It was electrifying in TOS and Enterprise.
The plot involves mirror-Kira squirming her way back into her masters' favours by obtaining cloaking devices that the Alliance already had. See in In A Mirror, Darkly and Through the Looking Glass. However I suppose this could be regarded as characterisation, re. Worf's stupidity. (After this, she was planning to promise him warp drive capability, phasers and shields.)
There's also a bit where Quark and Rom steal military equipment from the ship of one of Deep Space Nine's allies during a war. Is this taken seriously? Are we being encouraged to think that Quark might get imprisoned or even executed for this? Of course not.
Garak gets an amusing scene with Rom, but then afterwards an annoying one when being scammed by the Ferengi. Oh, and once again Star Trek can't bring itself to have consequences even when it's doing the last mirror universe episode in the last season of this show. Do the bad guys all get killed? No. Do the good guys all get killed? No. (I'd have liked that best, actually, since it would have given horrific consequences to Quark's actions and forced us to take this comic relief character seriously.) The good guys win, but most of the bad guys get lazy plot trapdoors to safety. One dies. That's it... well, apart from the mandatory "Let's Kill A Ferengi". Every time we've visited the mirror universe in Deep Space Nine, the show's killed a Ferengi. It's like the Star Trek equivalent of "the black character dies first."
Nicole de Boer is good. She's taking her new role seriously and she apparently had a blast with it, afterwards saying, "Can I play this character all the time?" Nana Visitor doesn't get much to play with, but she does manage to get a Star Trek episode going hog-wild with rampant lesbianism. Star Trek's traditionally been notorious for avoiding that sort of thing. (We also see Chase Masterson's cleavage.)
In principle, I really like this story. A hero visits the mirror universe to save his master... and it's Quark! The idea is strong. It's just that it's being hamstrung by the limpness of what's left of Deep Space Nine's mirror universe and by the characterisation of Rom (and to a less painful extent Zek). They might as well have been wearing clown shoes and had a swanee whistle after all their lines on the soundtrack. Apparently writer Ira Behr likes this episode because, through Rom, "We finally got to question the whole lunatic idea of the mirror universe." I didn't know Behr was mentally enfeebled. I can see the questioning he's talking about, but it's as challenging as a four-year-old who thinks it's funny to keep asking "why".
However there's also good stuff, if you can fight your way through the bad. I love Armin Shimerman. That's better than it could have been.