Short version, based on having seen the first 26 episodes: Overall, it's great.
Longer version: I think the GitS manga has some great ideas, but is incomprehensible. I think the GitS movie is lovely, but dull. Fortunatly, Stand Alone complex combines the best of both worlds, with top notch animation, really solid writing, and a terrific sense of design...except for whoever decided that the Major shouldn't wear any pants. Her outfit is god-awful.
The series is split not-quite 50/50 between "stand alone" one-shots and "complex" story-arc episodes about the enigmatic Laughing Man. The one-shots vary wildly and range from subpar to pretty damn great. (Any episodes featuring the Tachikomas - goofy sentient tanks - definately fall in the great category.) The complex episodes, however, are uniformly terrific, with a mix of action, political intrigue, and just a touch of philisophical wanking. Unlike Oshii's stab at this combination, GitS:SAC doesn't make me fall asleep. GitS:SAC also gets bonus points for featuring my second favorite name-drop in anime, which takes place in episode 26.
So, yeah - overall, it's great, though a few episodes are clunkers. I haven't seen enough of the second season to comment, but if it's anything like the first 26 episodes, I expect it to be damn good. The single disc US DVD release looks to be a perfectly solid buy, though the special edition isn't what I'd call a deal.
Oh, and Matlock: dunno what you heard about the change in the opening sequence, but it's a truly minor detail. Basically, the CG heavy opening sequence wasn't ready until episode 3, so they threw together a temp opening. Fanboy whining about how the original opening was cut is just that - fanboy whining.
FnordChan