This was one of the better episodes of Season 5. Of course, that's not saying much: We're only 4 episodes into the season, and I didn't think #2 (The Seed) and #3 (Broken Ties) were particularly good.
(Broken Ties provided closure for Ronon's previous episode with Tyre, Reunion, which was nice, but when the Season 5 DVD comes out, it's not like I'm going to watch that episode more than once. I didn't think The Seed was very good at all.)
I am a fan of shows that have season-long arcs. For example, I enjoyed how Buffy the Vampire Slayer had a "big bad" each season, and I've enjoyed the long-term stories that have been introduced on Atlantis (such as the Michael story arc). I like the suspense of a long story unfolding, I like watching episodes for clues and tidbits about the arcs, and and I like trying to predict what will happen. I also like episodes that contribute to the overall mythology of a series. (I think what I "really" like is re-watching episodes and realizing that some tidbit actually turned out to be important.) So, when I watch stand-alone episodes, I have very high expectations for them: They either need to be interesting or useful.
In order to be interesting, the adventure itself needs to be fun, suspensful, and worthwhile. On a show like Atlantis, unless the doctor is in peril, we know that there's a good chance the heroes are going to survive. (If Joss Whedon ever writes or directs an episode, worry! ;) ) Since there's no threat of death/damage/severe injury, what compels us to watch? Do the characters learn something about each other? Do the characters learn something about themselves? Do we learn something about them? For example, Trio provided the characters with a chance to bond with each other and be resourceful in a non-scifi situation, and Tao of Rodney showed us what kind of person Rodeny is deep down.
In order to be useful, the heroes need to come back with knowledge or technology they can use later on. For example, I thought Inferno was an average episode, but they came back with The Orion, which was important later on.
Getting back to The Dadealus Variations, I found the "interestingness" of the episode fairly average. I was obviously not concerned that the characters might not make it out alive. We knew Rodney would find a way to get them back in the episode's 42(ish) minute timeframe. I don't recall learning much about the characters, other than Ronon's blasé attitude about their alternate selves. Seeing Atlantis' planet in other realities was interesting, although this appears to be of little consequence in the grand scheme of things.
I think it would've been more interesting if the team got stuck in one of the alternate realities, and an alternate "A-team" had to get them back, somewhat of a reversal of what happened in McKay and Mrs. Miller. That way, for once, "our" Atlantis wouldn't be the smartest A-team out there; they'd have to rely on someone else for a change. Imagine if an alternate Zelenka sent them back! Or, what if an alternate Lorne were in charge of Atlantis? Or, look at what happened in the SG-1 episode The Road Not Taken, where Carter got thrown into an alternate universe, and they didn't want to send her back? Imagine an alternate Atlantis deciding they were too useful to give up (perhaps due to the war with the unknown new aliens we saw in the episode), refusing to send them back, and our A-team fighting against alternate versions of themselves, in order to get back into their correct universe?
The most useful thing about this episode is that Rodney comes back with the specs to make an alternate reality drive. Sure, Sheppard forbids him to make one, but as the Gateworld analysis points out, Woolsey or the IOA might have other ideas.
The episode's big mistake was the lack of follow up on the hostile aliens that the team encountered in the alternate reality. I kept expecting Sheppard to at least make a reference to them upon returning, such as, "We need to figure out who those aliens are so we can be ready for them if they show up in our reality."
The thing I disliked most about the episode was the, um, Sheppard-wank at the end (when Sheppard talked to alt-Sheppard). And would it really have hurt him to say, "We're just passing through from an alternate dimension"? I don't see why he had to be so coy about who they were and where they came from. For that matter, ISTR alt-Sheppard said that the Daedalus had been destroyed. Shouldn't he have been demanding to know who they were? (Or, you know, suspected that they were from an alternate reality and said as much?)
Overall, I give it 7/10.
 Perhaps this episode is leading into a season-long arc or is contributing to the series' mythology, and I just don't know it yet.
 Since Rodney got them back by basically reversing the alternate reality drive's course, obviously getting help from an alternate Atlantis would've been out of the question... unless McKay shut off the drive to buy time to think, and it took an alterante A-team to help him fix it...
 If they did something like this, no doubt I'd complain that it was too similar to the SG-1 episode, and why couldn't the writers come up with something original? Some people are just never happy. ;)