I previously posted about Stargate SG-1 and when it finally left the air after 10 years. This Stargate spin-off was not "as good" as the original to a lot of people. There was a definite following with Richard Dean Anderson as O'Neill in the original series.
This season, I think some of the folks from the original show have come over to Atlantis - writing-wise.
It seems a little lighter, with more character development now. More relationships, etc.
A big change was bringing Amanda Tapping over from the original show. She doesn't get as much screen time now as she did, but I'm sure she'll be more involved over time.
They have also added Jewel Staite (from Firefly/Serenity) this season, and she's fun as well.
One thing I love about these shows is that my kids also enjoy them so much. Trevor catches it at college and Diana watches it with us.
My favorite character is McKay (looks annoyed), the Canadian, he's played by David Hewlett. We also like Ronon (the tall guy with dreads), played by Jason Momoa. He's getting the best lines now.
Teyla (Rachel Luttrell) is having a baby soon, and there's a whole plotline about her missing people and the father of her child.
And then there's Col. John Sheppard (Joe Flanigan), who is the cool, soldier-guy who doesn't play by the same rules as everyone else.
I hope this series can last a long time yet - I see it getting better and more fun to watch. Plus I don't know how things turn out every time. Occasionally someone gets killed off -- that's why there are two new characters this season (not that that means anything - Daniel Jackson in SG-1 got killed more times than any other character in TV history I think...he was killed or presumed dead 20 times!).
I look forward to Fridays on Sci-Fi :)