This brief introduction will contain spoilers on the 6th and 7th seasons of Stargate SG-1 and the first two episodes of Stargate Atlantis. It also requires knowledge of the common concepts of Stargate SG-1. At the time of writing, five episodes of Atlantis have been aired. The series premiered on Friday, 16th of July 2004, on the Sci-Fi Channel.
Stargate begat Stargate SG-1, Stargate SG-1 begat Stargate Atlantis
In seasons six and seven of Stargate SG-1, the main villain was the not quite, but almost ascended Goa'uld Anubis. To counter Anubis' command of the Ancients' technology, the ascended Daniel Jackson told SG-1 of the Lost City of the Ancients, which would contain ancient weapons and various other nice gadgets that would help save the world.
As we witnessed in the season 7 finale, the place finally discovered on Antarctica was but an outpost of the Lost City which remained pretty lost. The title of the series, of course, already gives away what the Lost City was called. Where it is, however, isn't found out until the first episode of Stargate Atlantis. The Ancients of Earth plagued by an illness beyond their healing abilities departed the planet to another world in a galaxy called Pegasus, hundreds of thousands of light years away.
Doctor Jackson is able to recover the gate address of the Lost City, which consists of eight symbols, like the intergalactic address that O'Neill used to contact the Asgard when he was forcefed a databank of the Ancients many, many seasons ago. There is a catch, however: you need a heck of a lot of energy for a wormhole that long. A simple naquada reactor won't cut it: you need one of those Ancient power sources (called Zero Point Modules, or ZPMs).
Stargate Command only has one ZPM at their disposal, and the trip will drain it, so a one way expedition through the Stargate is undertaken. Its mission is to recover more Ancient technology for the inevitable conflicts with the Replicators lead by the vengeful Fifth and the rising star of the Goa'uld System Lords, Bhaal. The expedition won't be able to gate back to the Milky Way for quite a while, at least until they can recover more ZPMs, so a spin-off series is needed.
Accents, Colours, Uniforms
The creators of Stargate Atlantis have been very careful to strike a balance between being different enough that Atlantis and SG-1 can't be mixed up with each other, but similar enough that the spin-off won't get a life of its own. This is evident in visual design: the Stargates of the Pegasus galaxy are a seemingly modernised version of the Milky Way gates, with blue and green hues instead of gray and red, and a new, snazzier dialing sequence: think of the difference between a rotary phone and a button phone. Even the wormhole sequence is different.
What's more, the expedition is nothing like the USAF-run Stargate Command. Lead by Doctor Elizabeth Weir, who already made her appearance in Stargate SG-1, the team consists of a detachment of Air Force troops and a flock of scientists from all corners of the world. Every able nation wants its share of the pie now that the incident with Anubis on Earth orbit has forced the United States to reveal the Stargate program to other governments. This contributes to both the appearance of the series, with brand new uniforms (although Dr. Weir seems to have a different set of clothes in every episode), and the characters.
Major John Sheppard (played by Joe Flanigan) is the leader of the crack team of four people, "Atlantis-1" in a way, who do the bulk of the excursions, usually the most dangerous ones. Sheppard didn't know about the Stargate program until a few weeks ago and is still digesting the fact. As a character, so far he's been pretty much "the O'Neill" of SGA, never leaving anyone behind, respecting the same kind of honour code of the soldier. What makes him special is that thanks to his DNA he can operate Ancient vehicles with just his thoughts.
Teyla (played by Rachel Luttrell) is one of technologically regressed natives of the galaxy, descendants of the Ancients. Teyla is the "the Teal'c" of SGA, an excellent warrior, knowing the ways of the new peoples they'll meet, and the myths surrounding things. She trusts her own kind blindly and seems to have a thing going on with Sheppard. Fans of romantic twists and turns will probably have their hearts content, which wasn't possible with the professionals of SG-1.
Doctor Rodney McKay (played by David Hewlett) is the chief scientist, with the smarts of both Sam Carter and Daniel Jackson rolled into one person, who knows it and behaves accordingly. Familiar from his constant bickering with Carter in SG-1, he is an arrogant son of a bitch, and by no means typical hero material. He is selfish, and gets afraid - not that he admits it. The focus of most of the humour so far, McKay's character has promise to be an interesting change to your average protagonist. There's the risk that the writers will make him more tolerable later on, though.
Lieutenant Aiden Ford (played by Rainbow Sun Francks) is another soldier, a rather reckless person, but whose role has so far been to escort people and to provide cover. His character, thus, has so far felt like a "token black" role, but hopefully this will change as the show progresses. In the SG-1 comparison he really has no SG-1 equivalent: the slots for Carter's and Jackson's brain are taken, so are Teal'cs and O'Neill's, so all that's really left are Carter's fighting skills. Not much to base a character on, unless the writers can build up a different group dynamic from SG-1. And that is to be hoped for, because with McKay this is not a team that can become almost a family the same way SG-1 has become over the years.
Listed on the Atlantis web site at scifi.com as a part of "the new team", Doctor Elizabeth Weir (played by Torri Higginson) has spent most of her time running the new command centre in the City of Atlantis like the expedition leader should. While a civilian, she has a certain military flavour to her command: she wants the job done, period, and she won't tolerate insubordination. She is also willing to take risks to get her people back in one piece, making for an empathic but not necessarily an efficient commander. Despite the "Dr." in front of her name, she's "the Hammond" of SGA.
Another recurring character has so far been Doctor Carson Beckett (M.D., played by Paul McGillion), whose most prominent aspect has been his blatant Scottish accent. Apparently to the writers this is cultural diversity: all of the other main characters from Earth are from English-speaking countries as well. Weir, Sheppard and Aidan are from the US, McKay is from Canada. "It's a diverse group, we need someone exotic and we need the MD... I know, a Scotsman!" The actual foreigner spots have been reserved for random scientists some of whom don't even speak English.
Quite a Bit of Potential
Despite the mock internationality of the explorers - which can still change, of course - Stargate Atlantis has a lot of potential to become an interesting show on its own might. Basing it off Stargate SG-1 has its ups and downs. Many concepts need not explaining, but that means knowledge of SG-1 is required to make anything out of it. The scenario of being stranded on a different galaxy rules out irritating politicians trying to hijack the program, and we can concentrate on exploration and research.
The Lost City, as the expedition arrives to it, is vacant and empty, so they appropriate it for their own use. A hologram left by the former tenants speaks of a scourge called "the Wraith" which has all but eradicated the Ancients and reduced them to the level of domesticated cattle. Yes, cattle. The Wraith, a species of pale human-like creatures with long hair and two small mandibles on their face, feed on life forms, and humans are their favourite treat.
This makes for a rather intriguing hunter-prey situation. The villains are, of course, absolutely evil just like the Goa'uld. Not to be trusted, or negotiated with, just eliminated. Of course, you can't eliminate a Wraith, they keep regenerating no matter how many P90 rounds you pump into them. The Ancients were no match to the Wraith, how can the Earthlings survive?
This creates an atmosphere familiar from the first few seasons of SG-1. The Bad Guys are there, they are coming out in strength, they will come for us, and there is nothing we can do about it. It's a race against time to find a way to counter their inevitable attack. Even Earth is in jeopardy, if the Atlantis Gate is to fall to the hands of the Wraith - it's apparently the only one capable of dialing to Earth. They are salivating over the prospect of a feeding ground of six billion.
With the mandatory guest appearances of Jack O'Neill and Daniel Jackson out of the way in episode one, with Earth out of reach, the series can leave behind all that and face what is literally a galaxy of possibilities. Some clever new tricks have been showcased, for instance, Stargates are used for space travel, either with Wraith fighters or little Ancient ships called "Puddlejumpers". The Wraith have a lot of meat in them to become as intricate and detailed as the now familiar Goa'uld, and there is much new technology to be had. References to Earth mythology should also be entirely shed, as the Ancients populated Pegasus several millions of years ago.
With new and good science fiction shows being rare these days, Stargate Atlantis is more than enough, and can become as good as its cousin SG-1. It took a few seasons for SG-1 to grow to be the fun and interesting show it is now, one you keep coming back to, and if Atlantis can survive that necessary stage it can become an equally great show. There's no reason to think it won't: the show is raking in as much or even more viewers than SG-1. If you are a fan of Stargate SG-1 but haven't checked out Atlantis yet, where the heck have you been? Tune in now.