Ironically, we were only watching the series as current television was on hiatus, but now that they've returned, we're still watching Atlantis. Even though I believe we are in a platinum age of television, with actually too many amazing shows, dazzling plot lines, and fantastic characters to follow, Atlantis really hit a sweet spot for us. It managed to walk that fine line between being campy and intense while giving interesting characters (after Ford disappears) and some thought-provoking science fiction. Better still, even the younger boys are hooked (despite some occasionally scary bad guys). Sadly, at the pace that we're going, we will probably run through the entire show pretty soon as it only went for five season with each season set at twenty episodes.
After Firefly, I think I place it as my second-favorite sci-fi show. Both Battlestar and DS9 get a little too weird near the end of their runs which keep them at 3rd and 4th (respectively). Granted, there's a lot of sci-fi that I haven't seen, and some of the newer shows have had amazing concepts, so mine should not be counted as a definitive ranking. Still, if you haven't seen the show, it's worth the time.