Should've stopped after the second one.
What was with Sisko sleeping with Mirror Kira and Jadzia? Wouldn't that be awkward when he got home.
And the copy of the Defiant was a bit much.
Missed opportunity to see what MU Romulans were like.
I'm in complete agreement. Especially about the Defiant... wow, they have the ability to replicate the whole thing in record time, but then can't quite get the structural integrity right? It's like building the World Trade Center from scratch and then not knowing how to correct flaws with the elevator shafts. And then, why build just one? Why not two or three?
Also, I never quite get it... at one point they're down to practically no shields, "the next shot will destroy us", and nobody seems seriously worried--not even Sisko. Yes, he's an excellent pilot, but I didn't detect any nervousness on his part. It just didn't feel plausible to me. And yes, they flew close to the hull of the Klingon cruiser because the surface guns couldn't move fast enough, but towards the end you see the Defiant at some distance away--one shot and they've have had it.
And another thing: In the mirror universe, personalities are very different. True, there are underpinnings of similarities, but generally everyone is supposed to be emotionally opposite. Nice people are nasty, the confident are meek, the cordial are unruly... I guess it's not a
complete reversal across the board, but I'd have expected Jennifer not to be as soft and endearing. Bashir was definitely a complete opposite. O'Brien? He became the
same O'Brien as in the 'normal' universe... I couldn't tell them apart.
Lastly, we have this 'security breach', where the technology is developed to enable universe-to-universe transport. O'Brien is able to do this on his own without any help. So... wouldn't other more skilled people have come up with it as well? Even still... wouldn't it create a serious breach of security? You'd think that the next most important thing to do would be to create some kind of energy barrier that prevents them from coming through. Or go back to destroy the technology that has been developed so that they don't keep coming through. If the Mirror universe is deviant, wouldn't you think the people there would exploit this "hole"? Come on over to the 'positive' universe, steal stuff, then return back home? I smell a massive gap in plausibility here.
So... although I did enjoy the first two episodes, I thought that those which followed were not handled well and left too many loose threads dangling.