I hated that plot line. The moment alternate universe travel becomes casually possible, all tension leaves the plot. No matter what happens you can now undo it.
It wasn't
casual alternate universe travel. The drive itself was malfunctioning and led to one version of the Atlantis team's death. Traveling to alternate universes doesn't really undo things anyways. A quantum replacement of someone dead is still just a replacement. (RIP the main universe's
Harry Kim.) The same with a clone.
Like, if the Earth was destroyed by the Goa'uld, the Replicators, the Ori, or the Wraith; fleeing to an alternate universe where that didn't happen, doesn't mean that original Earth isn't dead. I would have loved if they kept the alternate universe
Sam around because a character suddenly having a dimensionally displaced twin is an interesting concept to explore. So I always
hated the bullshit
Entropic Cascade Failure thing you can just tell the writers invented on the spot to get rid of her. And this condition is also never
relevant ever again the next time alternate universe versions meet each other.
Beyond that, alternate universes can also have adverse effects on the main universe! Like
how the Wraith finally found where Earth exactly is in season 5.
Now, what really undoes things is, explicitly, time travel. Stargate has,
on a few occasions, already undid very bad ends with casual time-travel. That's way more egregious than alternate universes in my mind. At least the
bad guys use the reset button at least once.
But to be honest, I don't really feel tension when watching shows with multiple seasons anymore. The draw for me is the characters and the worldbuilding, not "Will this protagonist coded character succeed or fail at their objectives?" At a default, going into pretty much any form of fiction, I can assume "Our main characters will win at the end of the day" and be right 95% of the time. So... there's not a lot of tension unless my assertion is proven wrong, and those few shows aren't necessarily better to me.
It's not the mystery of what's at the end of the road that gets me to keep watching/reading, it's how enjoyable the journey is on the way.